scholarly journals A Fast Calibration Method for Phased Arrays by Using the Graph Coloring Theory

Sensors ◽  
2018 ◽  
Vol 18 (12) ◽  
pp. 4315 ◽  
Author(s):  
Lijie Yang ◽  
Ruirui Dang ◽  
Min Li ◽  
Kailong Zhao ◽  
Chunyi Song ◽  
...  
Keyword(s):  
Graph Coloring ◽  
Large Scale ◽  
Phased Array ◽  
Phased Arrays ◽  
Calibration Method ◽  
Omnidirectional Antenna ◽  
Phase Errors ◽  
Calibration Problem ◽  
Calibration Methods ◽  
Calibration Time

Phased array radars are able to provide highly accurate airplane surveillance and tracking performance if they are properly calibrated. However, the ambient temperature variation and device aging could greatly deteriorate their performance. Currently, performing a calibration over a large-scale phased array with thousands of antennas is time-consuming. To facilitate the process, we propose a fast calibration method for phased arrays with omnidirectional radiation patterns based on the graph coloring theory. This method transforms the calibration problem into a coloring problem that aims at minimizing the number of used colors. By reusing the calibration time slots spatially, more than one omnidirectional antenna can perform calibration simultaneously. The simulation proves this method can prominently reduce total calibration time and recover the radiation pattern from amplitude and phase errors and noise. It is worth noting that the total calibration time consumed by the proposed method remains constant and is negligible compared with other calibration methods.

scholarly journals Cobot User Frame Calibration: Evaluation and Comparison between Positioning Repeatability Performances Achieved by Traditional and Vision-Based Methods

Robotics ◽  
2021 ◽  
Vol 10 (1) ◽  
pp. 45
Author(s):  
Roberto Pagani ◽  
Cristina Nuzzi ◽  
Marco Ghidelli ◽  
Alberto Borboni ◽  
Matteo Lancini ◽  
...  
Keyword(s):  
Quantitative Analysis ◽  
Production Line ◽  
Calibration Method ◽  
Fiducial Marker ◽  
Positioning System ◽  
Local Calibration ◽  
Calibration Methods ◽  
Robot Positioning ◽  
Good Repeatability ◽  
Calibration Time

Since cobots are designed to be flexible, they are frequently repositioned to change the production line according to the needs; hence, their working area (user frame) needs to be often calibrated. Therefore, it is important to adopt a fast and intuitive user frame calibration method that allows even non-expert users to perform the procedure effectively, reducing the possible mistakes that may arise in such contexts. The aim of this work was to quantitatively assess the performance of different user frame calibration procedures in terms of accuracy, complexity, and calibration time, to allow a reliable choice of which calibration method to adopt and the number of calibration points to use, given the requirements of the specific application. This has been done by first analyzing the performances of a Rethink Robotics Sawyer robot built-in user frame calibration method (Robot Positioning System, RPS) based on the analysis of a fiducial marker distortion obtained from the image acquired by the wrist camera. This resulted in a quantitative analysis of the limitations of this approach that only computes local calibration planes, highlighting the reduction of performances observed. Hence, the analysis focused on the comparison between two traditional calibration methods involving rigid markers to determine the best number of calibration points to adopt to achieve good repeatability performances. The analysis shows that, among the three methods, the RPS one resulted in very poor repeatability performances (1.42 mm), while the three and five points calibration methods achieve lower values (0.33 mm and 0.12 mm, respectively) which are closer to the reference repeatability (0.08 mm). Moreover, comparing the overall calibration times achieved by the three methods, it is shown that, incrementing the number of calibration points to more than five, it is not suggested since it could lead to a plateau in the performances, while increasing the overall calibration time.

Ultrasonic Testing of Railway Transport Units with Phased Array Flaw Detectors

NDT World ◽  
2015 ◽  
Vol 18 (3) ◽  
pp. 72-76 ◽  
Author(s):  
Макарова ◽  
Taisiya Makarova ◽  
Мелешко ◽  
Nataliya Meleshko ◽  
Жаринов ◽  
...  
Keyword(s):  
Large Scale ◽  
Phased Array ◽  
Phased Arrays ◽  
Surface Profile ◽  
Piezoelectric Transducers ◽  
Back Surface ◽  
Railway Transport ◽  
Transverse Cracks ◽  
Testing Procedures ◽  
Standard Testing

The article describes possibilities of phased array flaw detectors application for testing of railway transport units, such as wheel set axles, all-rolled wheels, solebars of freight cars. The task was to reproduce the standard testing procedures using phased array flaw detectors and demonstrate their advantages in visibility, efficiency, repeatability, results validity. Unfortunately, one of the main advantages of phased array flaw detectors, namely – a possibility to control the focusing depth – are lost while testing of large scale objects. Sector scanning technique with the phased array flaw detectors OmniScan and Isonic 2010 in the minimum configuration was used for the research. In the all cases acoustical images of the following reflectors were obtained within the range of selected angles: saw-cuts in axles, spot-drillings and saw-cuts in wheels, side drilled holes and natural defects in solebars. The Multi Group software (Isonic 2000) at testing of wheel set axles has enabled the testing schemes to be realized with one prism and one phased array instead of several classical piezoelectric transducers. Circumferential testing of all-rolled wheels from internal lateral surface under the roll surface level has allowed transverse cracks and flange embedded defects to be detected. Solebar testing has been more complicated because of a form and irregularity of scanning surface, necessity of its cleaning and a complex profile of back surface. Nevertheless the usage of phased array flaw detectors has made it possible to identify the back surface profile. Application of phased arrays substantially increases testing efficiency and improves visibility of obtained results.

scholarly journals On-Site Calibration Method for Line-Structured Light Sensor-Based Railway Wheel Size Measurement System

Sensors ◽  
2021 ◽  
Vol 21 (20) ◽  
pp. 6717
Author(s):  
Yunfeng Ran ◽  
Qixin He ◽  
Qibo Feng ◽  
Jianying Cui
Keyword(s):  
Structured Light ◽  
Field Tests ◽  
Calibration Method ◽  
Field Application ◽  
Calibration Error ◽  
Epipolar Constraint ◽  
Calibration Process ◽  
Calibration Methods ◽  
Calibration Accuracy ◽  
Calibration Time

Line-structured light has been widely used in the field of railway measurement, owing to its high capability of anti-interference, fast scanning speed and high accuracy. Traditional calibration methods of line-structured light sensors have the disadvantages of long calibration time and complicated calibration process, which is not suitable for railway field application. In this paper, a fast calibration method based on a self-developed calibration device was proposed. Compared with traditional methods, the calibration process is simplified and the calibration time is greatly shortened. This method does not need to extract light strips; thus, the influence of ambient light on the measurement is reduced. In addition, the calibration error resulting from the misalignment was corrected by epipolar constraint, and the calibration accuracy was improved. Calibration experiments in laboratory and field tests were conducted to verify the effectiveness of this method, and the results showed that the proposed method can achieve a better calibration accuracy compared to a traditional calibration method based on Zhang’s method.

An improved gain-phase error self-calibration method for robust DOA estimation

2018 ◽  
Vol 11 (2) ◽  
pp. 105-113 ◽  
Author(s):  
Wencan Peng ◽  
Chenjiang Guo ◽  
Min Wang ◽  
Yuteng Gao
Keyword(s):  
Covariance Matrix ◽  
Phase Error ◽  
Iteration Process ◽  
Doa Estimation ◽  
Calibration Method ◽  
Coherent Signals ◽  
Source Power ◽  
Phase Errors ◽  
Calibration Methods ◽  
Exchange Matrix

AbstractA novel online antenna array calibration method is presented in this paper for estimating direction-of-arrival (DOA) in the case of uncorrelated and coherent signals with unknown gain-phase errors. Conventional calibration methods mainly consider incoherent signals for uniform linear arrays with gain-phase errors. The proposed method has better performance not only for uncorrelated signals but also for coherent signals. First, an on-grid sparse technique based on the covariance fitting criteria is reformulated aiming at gain-phase errors to obtain DOA and the corresponding source power, which is robust to coherent sources. Second, the gain-phase errors are estimated in the case of uncorrelated and coherent signals via introducing an exchange matrix as the pre-processing of a covariance matrix and then decomposing the eigenvalues of the covariance matrix. Those parameters estimate values converge to the real values by an alternate iteration process. The proposed method does not require the presence of calibration sources and previous calibration information unlike offline ways. Simulation results verify the effectiveness of the proposed method which outperforms the traditional approaches.

Ultrasonic Testing of Railway Transport Units with Phased Array Flaw Detectors. Part 2

NDT World ◽  
2015 ◽  
Vol 18 (4) ◽  
pp. 76-80
Author(s):  
Сойфер ◽  
Yuriy Soyfer ◽  
Макарова ◽  
Taisiya Makarova ◽  
Мелешко ◽  
...  
Keyword(s):  
Ultrasonic Testing ◽  
Large Scale ◽  
Phased Array ◽  
Phased Arrays ◽  
Surface Profile ◽  
Back Surface ◽  
Railway Transport ◽  
Complex Profile ◽  
Testing Procedures ◽  
Standard Testing

The second part of the article describes possibilities of phased array flaw detectors application for testing of railway transport units, such as solebars of freight cars. The task was to reproduce the standard testing procedures using phased array flaw detectors and demonstrate their advantages in visibility, efficiency, repeatability, results validity. Unfortunately, one of the main advantages of phased array flaw detectors, namely – a possibility to control the focusing depth – is lost while testing of large scale objects. Sector scanning technique with the phased array flaw detectors OmniScan and Isonic 2010 in the minimum configuration was used for the research. In the all cases acoustical images of the side drilled holes and natural defects in solebars were obtained within the range of selected angles. Solebar testing has been more complicated because of a form and irregularity of scanning surface, necessity of its cleaning and a complex profile of back surface. Nevertheless the usage of phased array flaw detectors has made it possible to identify the back surface profile. Application of phased arrays substantially increases testing efficiency and improves visibility of obtained results.

A new calibration method for gravity meters

Geophysics ◽  
1991 ◽  
Vol 56 (5) ◽  
pp. 701-704 ◽  
Author(s):  
Lucien LaCoste
Keyword(s):  
Calibration Curve ◽  
Calibration Method ◽  
New Method ◽  
Micrometer Screw ◽  
Calibration Methods ◽  
Calibration Time ◽  
Calibration Interval

Current calibration methods give gravity meter accuracies of 3 to 5 μGal [Formula: see text] over 10 mGal intervals. The new calibration method should extend the accuracies to 100 mGal intervals. The new method nulls with both a micrometer screw and an electrostatic feedback nuller. The screw is calibrated and used only at discrete points and the electrostatic nuller completes the nulling to obtain gravity readings. Determining the calibration curve itself rather than measuring and integrating calibration (interval) factors avoids approximations. Circular errors (periods of the order of a turn of the screw) are completely taken into account at the discrete points. Calibration only at discrete points makes calibration time reasonable.

scholarly journals A Multi Camera and Multi Laser Calibration Method for 3D Reconstruction of Revolution Parts

Sensors ◽  
2021 ◽  
Vol 21 (3) ◽  
pp. 765
Author(s):  
Hugo Álvarez ◽  
Marcos Alonso ◽  
Jairo R. Sánchez ◽  
Alberto Izaguirre
Keyword(s):  
3D Reconstruction ◽  
Calibration Method ◽  
Laser Plane ◽  
Calibration Methods ◽  
Laser Calibration ◽  
Calibration Object ◽  
Focus Plane ◽  
Chessboard Pattern ◽  
Line Patterns

This paper describes a method for calibrating multi camera and multi laser 3D triangulation systems, particularly for those using Scheimpflug adapters. Under this configuration, the focus plane of the camera is located at the laser plane, making it difficult to use traditional calibration methods, such as chessboard pattern-based strategies. Our method uses a conical calibration object whose intersections with the laser planes generate stepped line patterns that can be used to calculate the camera-laser homographies. The calibration object has been designed to calibrate scanners for revolving surfaces, but it can be easily extended to linear setups. The experiments carried out show that the proposed system has a precision of 0.1 mm.

Stable Calibrations of Six-DOF Serial Robots by Using Identification Models with Equalized Singular Values

Robotica ◽  
2021 ◽  
pp. 1-22
Author(s):  
Zhouxiang Jiang ◽  
Min Huang
Keyword(s):  
Industrial Robot ◽  
Singular Values ◽  
Calibration Method ◽  
Identification Accuracy ◽  
Condition Numbers ◽  
Measurement Instruments ◽  
Unknown Parameters ◽  
Calibration Methods ◽  
Six Dof ◽  
The Stability

SUMMARY In typical calibration methods (kinematic or non-kinematic) for serial industrial robot, though measurement instruments with high resolutions are adopted, measurement configurations are optimized, and redundant parameters are eliminated from identification model, calibration accuracy is still limited under measurement noise. This might be because huge gaps still exist among the singular values of typical identification Jacobians, thereby causing the identification models ill conditioned. This paper addresses such problem by using new identification models established in two steps. First, the typical models are divided into the submodels with truncated singular values. In this way, the unknown parameters corresponding to the abnormal singular values are removed, thereby reducing the condition numbers of the new submodels. However, these models might still be ill conditioned. Therefore, the second step is to further centralize the singular values of each submodel by using a matrix balance method. Afterward, all submodels are well conditioned and obtain much higher observability indices compared with those of typical models. Simulation results indicate that significant improvements in the stability of identification results and the identifiability of unknown parameters are acquired by using the new identification submodels. Experimental results indicate that the proposed calibration method increases the identification accuracy without incurring additional hardware setup costs to the typical calibration method.

scholarly journals Vicarious Radiometric Calibration of Ocean Color Bands for FY-3D/MERSI-II at Lake Qinghai, China

Sensors ◽  
2020 ◽  
Vol 21 (1) ◽  
pp. 139
Author(s):  
Shengli Chen ◽  
Xiaobing Zheng ◽  
Xin Li ◽  
Wei Wei ◽  
Shenda Du ◽  
...  
Keyword(s):  
Infrared Imaging ◽  
Large Deviation ◽  
Ocean Color ◽  
Calibration Method ◽  
Surface Measurement ◽  
Radiometric Calibration ◽  
Lake Qinghai ◽  
Vicarious Calibration ◽  
Calibration Methods ◽  
Spectral Imager

To calibrate the low signal response of the ocean color (OC) bands and test the stability of the Fengyun-3D (FY-3D)/Medium Resolution Spectral Imager II (MERSI-II), an absolute radiometric calibration field test of FY-3D/MERSI-II at the Lake Qinghai Radiometric Calibration Site (RCS) was carried out in August 2018. The lake surface and atmospheric parameters were mainly measured by advanced observation instruments, and the MODerate spectral resolution atmospheric TRANsmittance algorithm and computer model (MODTRAN4.0) was used to simulate the multiple scattering radiance value at the altitude of the sensor. The results showed that the relative deviations between bands 9 and 12 are within 5.0%, while the relative deviations of bands 8, and 13 are 17.1%, and 12.0%, respectively. The precision of the calibration method was verified by calibrating the Aqua/Moderate-resolution Imaging Spectroradiometer (MODIS) and National Polar-orbiting Partnership (NPP)/Visible Infrared Imaging Radiometer (VIIRS), and the deviation of the calibration results was evaluated with the results of the Dunhuang RCS calibration and lunar calibration. The results showed that the relative deviations of NPP/VIIRS were within 7.0%, and the relative deviations of Aqua/MODIS were within 4.1% from 400 nm to 600 nm. The comparisons of three on-orbit calibration methods indicated that band 8 exhibited a large attenuation after launch and the calibration results had good consistency at the other bands except for band 13. The uncertainty value of the whole calibration system was approximately 6.3%, and the uncertainty brought by the field surface measurement reached 5.4%, which might be the main reason for the relatively large deviation of band 13. This study verifies the feasibility of the vicarious calibration method at the Lake Qinghai RCS and provides the basis and reference for the subsequent on-orbit calibration of FY-3D/MERSI-II.

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