Precise Position Measurement Research Articles

Visual-Inertial Fusion-Based Five-Degree-of-Freedom Motion Measurement System for Vessel-Mounted Cranes

Vessel-mounted cranes operate in complex marine environments, where precise measurement of cargo positions and attitudes is a key technological challenge to ensure operational stability and safety. This study introduces an integrated measurement system that combines vision and inertial sensing technologies, utilizing a stereo camera and two inertial measurement units (IMUs) to capture cargo motion in five degrees of freedom (DOF). By merging data from the stereo camera and IMUs, the system accurately determines the cargo’s position and attitude relative to the camera. The specific methodology is introduced as follows: First, the YOLO model is adopted to identify targets in the image and generate bounding boxes. Then, using the principle of binocular disparity, the depth within the bounding box is calculated to determine the target’s three-dimensional position in the camera coordinate system. Simultaneously, the IMU measures the attitude of the cargo, and a Kalman filter is applied to fuse the data from the two sensors. Experimental results indicate that the system’s measurement errors in the x, y, and z directions are less than 2.58%, 3.35%, and 3.37%, respectively, while errors in the roll and pitch directions are 3.87% and 5.02%. These results demonstrate that the designed measurement system effectively provides the necessary motion information in 5-DOF for vessel-mounted crane control, offering new approaches for pose detection of marine cranes and cargoes.

Scintillator-SiPM detector for tracking and energy deposition measurements

An innovative particle detector that offers a compelling combination of cost-effectiveness and high accuracy is introduced. The detector features plastic scintillators paired with a sparse arrangement of SiPMs, strategically positioned within a unique opto-mechanical framework. This configuration delivers precise measurements of spatial impact position and energy deposition of impinging particles. The manuscript describes the detector’s physical model complemented by an analytical representation. These calculations underpin a numerical algorithm, facilitating the estimation of particle impingement position and energy deposition. The results of the numerical calculations are compared with the output of GEANT4 simulations and evaluated by rigorous laboratory testing. An array of these detectors, intended for deployment in a spaceborne experiment, underwent detailed design, manufacturing, and testing. Their performance and alignment with the physical model were validated through meticulously conducted ground-based laboratory experiments, conclusively affirming the detector’s properties.

Self-calibratable absolute modular rotary encoder: a theoretical feasibility study

Abstract This paper introduces a self-calibratable absolute modular rotary encoder based on the Equal Division Average (EDA) method, designed to significantly enhance measurement accuracy and simplify installation. The proposed design integrates multiple optical sensors into the encoder stator Printed Circuit Board (PCB), enabling precise absolute position measurement through the averaging of sensors data. This multi-sensor approach compensates for alignment and installation inaccuracies, which are common issues in conventional modular encoders. To validate the design and predict encoder behaviour prior to manufacturing, a theoretical modelling of virtual optical sensors is performed. Based on experimentally collected cross-calibration data from a real optical encoder, this modelling framework enables to estimate the efficiency of self-calibration algorithm with sufficient accuracy and optimize the design and performance of the encoder. The obtained results confirm that the proposed measurement system significantly reduces error margin, improving the reliability and precision of position feedback. The initial position deviation of several hundreds of arcseconds might be reduced and kept below 8 arcseconds by using two or more additional optical sensors, even with the 0.5 mm misalignment of the encoder stator.

A cost-effective field-programmable-gate-array-based pulse processor for biomedical imaging applications

ObjectiveThis paper presents the design and evaluation of a cost-effective, high-spatial resolution, multichannel, field-programmable gate array (FPGA)-based readout system for Positron Emission Tomography (PET) detectors suitable for clinical and pre-clinical work in cancer and other diseases. A key challenge in PET imaging is the precise measurement of the time of arrival and energy of gamma photons originating from positron annihilation, along with the position of interaction within the detector. These parameters enhance image quality by improving coincidence detection, excluding Compton-scattered photons, and improving system spatial resolution. We developed a 16-channel readout system using single silicon photomultiplier (SiPM) element readout for efficient and precise energy, time, and position measurements. Each channel incorporates an FPGA-based sigma-delta analog-to-digital converter (ΣΔ-ADC) and tapped delay line (TDL) based time-to-digital converter (TDC) for timing and energy estimation. Performance characterization of the system was performed through simulation, electronically generated waveform, and actual PET detector signals from three different single scintillation crystals of face dimensions 3 × 3 mm2 and depths of 5 and 20 mm coupled to a 3 × 3 mm2 SiPM. We also constructed and tested a modular PET detector with a 10x10 array of 1.2x1.2x14 mm³ LSO crystals coupled to a 4x4 SiPM array of 3 × 3 mm2 elements. Best energy resolution was 9.3% at the 511 KeV photopeak and best coincidence timing resolution (CTR) was 210 ± 3.5 ps. Our system balances cost-effectiveness with performance and contributes to developments in PET signal acquisition and detector technology.

Simulation of time-crystal-like behavior for a few-boson chiral soliton model in a ring

We present numerical simulations for a chiral soliton model with N=2,3 bosons in a ring, which is a few-particle version of our previous mean-field model for a quantum time crystal. Following Syrwid, Kosior, and Sacha (SKS), the notion is that a precise position measurement of one particle can lead to spontaneous formation of a bright soliton that in a time crystal should rotate intact for at least a few revolutions around the ring. In their work SKS found spontaneous formation of a soliton due to the position measurement, but quantum fluctuations cause the soliton to subsequently decay before it has a chance to perform even one revolution of the ring. Based on this, they concluded that time-crystal dynamics are impossible for Wilczek's model of a bright soliton in a ring. In contrast, for our few-boson chiral soliton model, allowing for imprecise (weak) measurements of the particle position, we show that time-crystal-like behavior is possible, allowing for several revolutions of the spontaneously formed soliton around the ring. Published by the American Physical Society 2024

IStent insertion orientation and impact on trabecular meshwork motion resolved by optical coherence tomography imaging.

The iStent is a popular device designed for glaucoma treatment, functioning by creating an artificial fluid pathway in the trabecular meshwork (TM) to drain aqueous humor. The assessment of iStent implantation surgery is clinically important. However, current tools offer limited information. We aim to develop innovative assessment strategies for iStent implantation using optical coherence tomography (OCT) to evaluate the position and orientation of the iStent and its biomechanical impact on outflow system dynamics. We examined four iStents in the two eyes of a glaucoma patient. Three-dimensional (3D) OCT structural imaging was conducted for each iStent, and a semi-automated algorithm was developed for iStent segmentation and visualization, allowing precise measurement of position and orientation. In addition, phase-sensitive OCT (PhS-OCT) imaging was introduced to measure the biomechanical impact of the iStent on the outflow system quantified by cumulative displacement (CDisp) of pulse-dependent trabecular TM motion. The 3D structural image processed by our algorithm definitively resolved the position and orientation of the iStent in the anterior segment, revealing substantial variations in relevant parameters. PhS-OCT imaging demonstrated significantly higher CDisp in the regions between two iStents compared to locations distant from the iStents in both OD ( ) and OS ( ). Our proposed structural imaging technique improved the characterization of the iStent's placement. The imaging results revealed inherent challenges in achieving precise control of iStent insertion. Furthermore, PhS-OCT imaging unveiled potential biomechanical alterations induced by the iStent. This unique methodology shows potential as a valuable clinical tool for evaluating iStent implantation.

Dual UAV-based cross view target position measurement using machine learning and Pix-level matching

The measurement of target position in dual or multiple unmanned aerial vehicle (UAV) scenarios presents significant challenges, including data fusion for accurate location and depth determination, image matching difficulties and high computational requirements. This paper proposes a methodology for precise target position measurement in dual UAV-based cross view by employing the Zhang algorithm for camera calibration, the YOLOv8 network model for target detection and the SuperGlue algorithm for feature point extraction and registration. The methodology offers unique contributions to the literature on target position measurement using UAVs, including a novel approach for matching identical targets in different images and a method for measuring the position of shared targets in dual drone images within real space using a target pixel positioning matrix. The experimental results demonstrate the effectiveness of the proposed methodology in offering a promising and systematic solution for accurate and reliable target position measurement using dual UAVs.

Information entropies with Varshni-Hellmann potential in higher dimensions

This work investigates the behavior of Shannon entropy and Fisher information for the Varshni-Hellmann potential (VHP) in one and three dimensions using the Nikiforov-Uvarov method. We employ the Greene-Aldrich approximation scheme to obtain the energy eigenvalues and normalized wavefunctions, which are then used to calculate these information-theoretic quantities. Our analysis revealed remarkably similar high-order features in both position and momentum spaces. Notably, our calculations showed enhanced accuracy in predicting particle localization within position space. Furthermore, the combined position and momentum entropies obeyed the lower and upper bounds established by the Berkner-Bialynicki-Birula-Mycieslki inequality. Additionally, for three-dimensional systems, the Stam-Cramer-Rao inequalities were fulfilled for different eigenstates with respect to the calculated Fisher information. It is observed that as the position Fisher entropy decreases, indicating a more precise measurement of position, the momentum Fisher entropy must increase. This implies that the Fisher information regarding momentum decreases, resulting in a decrease in the precision of momentum measurement. This demonstrates how position and momentum uncertainties complement each other in quantum mechanics. Exploring the balance between position and momentum Fisher entropy reveals a fundamental aspect of the uncertainty principle in quantum mechanics, highlighting the restrictions on measuring certain pairs of conjugate variables simultaneously with high precision.

Vehicular Visible Light Positioning System Based on a PSD Detector.

In this paper, we explore the use of visible light positioning (VLP) technology in vehicles in intelligent transportation systems (ITS), highlighting its potential for maintaining effective line of sight (LOS) and providing high-accuracy positioning between vehicles. The proposed system (V2V-VLP) is based on a position-sensitive detector (PSD) and exploiting car taillights to determine the position and inter-vehicular distance by angle of arrival (AoA) measurements. The integration of the PSD sensor in vehicles promises exceptional positioning accuracy, opening new prospects for navigation and driving safety. The results revealed that the proposed system enables precise measurement of position and distance between vehicles, including lateral distance. We evaluated the impact of different focal lengths on the system performance, achieving cm-level accuracy for distances up to 35 m, with an optimum focal length of 25 mm, and under low signal-to-noise conditions, which meets the standards required for safe and reliable V2V applications. Several experimental tests were carried out to validate the results of the simulations.

Non-spherical Janus microparticles localization using equivalent geometric center and image processing

In recent years, Janus microspheres technology has been widely applied and developed in various fields. However, existing studies often rely on electron microscopy images, treating Janus microspheres as spherical to observe their submicron structures. This approach falls short in meeting the demand for precise measurement of the specific position and orientation of microspheres at the single-molecule scale. Here, we propose a standardized processing procedure that integrates multiple image processing algorithms to measure the position of Janus microspheres through the image capture. Our approach enhances the two-dimensional planar positioning accuracy of non-spherical Janus microspheres in micro-nano optical measurement systems. Utilizing this method, we can conduct a further research on the structure and motion characteristics of the microsphere at the single-particle scale. This method has been validated on a transmission illumination optical tweezers platforms, successfully calibrating the central position of the optical trap. Our work offers a greater convenience for measuring non-spherical Janus microspheres in liquid environments. It also provides a fresh perspective for subsequent studies on the motion trajectories and force dynamics of heterogeneous microspheres, showcasing its broad potential for application.

The breakup and instability structures of liquid jets in subsonic crossflows

The breakup of water and Jet A fuel jets injected transverse into elevated temperature (up to 425 °C), combustion pre-heated, subsonic crossflows was investigated by internally fluorescing the liquid jet column. The fluorescent dye seeded test liquids were illuminated by a pulsed laser light that was transmitted within the injector using a quartz rod light-guide. High-resolution images isolating the intact liquid column from light scattered by the surrounding dense spray facilitated precise measurement of the liquid column breakup position and the size and distribution of windward column instability waves. The injector geometry consisted of a 1 mm circular orifice with an orifice length of 20 mm with a tapered inlet. Liquid jet to gaseous crossflow momentum flux ratios were varied from 6 to 266 and the gas Weber number was varied from 10.7 to 228. Empirical correlations were derived for the liquid column breakup coordinates and breakup time in addition to the average and local maximum instability wavelength and amplitude on the liquid column windward surface. The reported correlations provided key insight into atomization physics and aim to support the quantitative validation of high-fidelity numerical simulations of the liquid jet in subsonic crossflow.

Feature information extraction method for narrow gap U-type groove based on laser vision

The precise measurement of weld groove position and geometric dimensions serves as the foundation for predicting and planning welding strategies and process parameters. The steep sidewalls of narrow gap U-type grooves pose challenges for sensing and detection during the welding process. This paper presents a feature information extraction method for narrow gap U-type grooves based on laser vision technology. Firstly, the image acquisition system is calibrated using the incident plane of the laser beam. Subsequently, a digital image processing technique is employed to enhance the collected images, combining a 3D spatial domain enhancement algorithm with a laser stripe image refinement method based on Euclidean distance transformation. Finally, the transverse and vertical positions of the groove, as well as its geometric features such as width, depth, assembly gap, and misalignment, are computed and measured using feature point positioning. The proposed algorithm is experimentally verified for its accuracy, robustness, and real-time performance. The results indicate that the method effectively suppresses unevenness in laser stripe brightness and mitigates random noise in the captured images. The average measurement errors for transverse position, vertical position, width, depth, assembly gap, and misalignment of the groove are 0.0857 mm, 0.0987 mm, 0.1664 mm, 0.2216 mm, 0.0935 mm, and 0.0997 mm, respectively. Furthermore, the average image processing time per frame is 58 ms, meeting the requirements of pre-weld detection in arc welding.

Measuring Point Planning and Fitting Optimization of the Flange and Spigot Structures of Aeroengine Rotors

An optimized measuring point planning and fitting method for rotor flange and spigot structures was proposed to achieve precise measurement of position and pose of the aeroengine rotors during docking processes. Firstly, the impact of circumferential phase angle, distribution range angle, total number of measuring points, and number of distribution rings on measurement uncertainty was analyzed. The measuring point planning schemes for flange and spigot were proposed. Secondly, the Gauss Newton iterative solution principle considering damping factors was clarified. Subsequently, an optimized iterative reweighting method consisting of weight iterative estimation, singular value detection under the Chauvenet criterion, and clustering detection was proposed for fitting the flange annular end face. A mapping point total least squares method with practical geometric significance was proposed for fitting the spigot cylinder face. Finally, measuring and fitting experiments were performed. The singular measuring point detection methods were verified. Under the optimized fitting methods, the goodness of fit and average orthogonal distance of flange and spigot structures are 0.756 and 0.089 mm, respectively, which have higher fitting accuracy than the other traditional methods.

Image Mapping Accuracy Evaluation Using UAV with Standalone, Differential (RTK), and PPP GNSS Positioning Techniques in an Abandoned Mine Site.

Global navigation satellite systems (GNSSs) provide a common positioning method that utilizes satellite signals to determine the spatial location of a receiver. However, there are several error factors in standalone GNSS positioning due to instrumental, procedural, and environmental factors that arise during the signal transmission process, and the final positioning error can be up to several meters or greater in length. Thus, real-time kinematic (RTK) correction and post-mission precise point positioning (PPP) processing technologies are proposed to improve accuracy and accomplish precise position measurements. To evaluate the geolocation accuracy of mosaicked UAV images of an abandoned mine site, we compared each orthomosaic image and digital elevation model obtained using standalone GNSS positioning, differential (RTK) GNSS positioning, and post-mission PPP processing techniques. In the three types of error evaluation measure (i.e., relative camera location error, ground control points-based absolute image mapping error, and volumetric difference of mine tailings), we found that the RTK GNSS positioning method obtained the best performance in terms of the relative camera location error and the absolute image mapping error evaluations, and the PPP post-processing correction effectively reduced the error (69.5% of the average total relative camera location error and 59.3% of the average total absolute image mapping error) relative to the standalone GNSS positioning method. Although differential (RTK) GNSS positioning is widely used in positioning applications that require very high accuracy, post-mission PPP processing can also be used in various fields in which it is either not feasible to operate expensive equipment to receive RTK GNSS signals or network RTK services are unavailable.

Parasitic time-grating angular displacement sensor for precision position measurement of turntable bearing

This paper proposes a parasitic time-grating angular displacement sensor for detecting the position of the turntable bearing. The sensor is mainly composed of probe, rotor, and supporting signal circuit. The probe consists of two separated measuring units on the left and right, and each measuring unit is composed of four sensing units with iron cores, excitation windings, and induction windings arranged according to specific rules. The rotor is made of sinusoidal isometric grooves based on the bearing end cover of the original turntable bearing. The signal processing circuit is used to filter, amplify, and compare the induction signal; meantime, it can generate the excitation signal. The high-frequency clock pulse signal is used as the measurement benchmark to realize the analysis of the position information of the induction signal. The structure and working principles of the sensor are presented in detail. Through the finite element method simulation, the feasibility of sensor scheme is verified, and the theoretical resolution of the prototype sensor is estimated to be about 1.33e−5. A sensor prototype is designed for testing, and the experimental results show that its accuracy can reach −0.003611° to 0.002583° in the range of [0°, 360°] after compensating the error point-by-point through the look-up table method.

Gamma Scientific Sets High Standards for Light Measurement

Gamma Scientific Sets High Standards for Light Measurement

Frequency-scanning interferometry for axial clearance of rotating machinery based on speed synchronization and extended Kalman filter

Rotor-stator axial clearance is a crucial design parameter affecting rotating machines' efficiency and safety. To realize accurate dynamic axial clearance measurement in high-speed rotating machinery with frequency-scanning interferometry (FSI), this paper proposes a novel algorithm of Doppler error suppression. By introducing rotor speed simultaneously as a Kalman filter parameter, the extended Kalman filter model is constructed by combining the a-priori information of rotating machinery. The feasibility is tested and verified by both simulation and experiment. This algorithm can suppress the Doppler error in FSI measurement and separate the axial movement and end face runout in real-time. Under laboratory conditions, a position measurement precision of ±3.5μm was achieved for rotation speed changing around 2400rpm.

A Mixed Hardware-Software Implementation of a High-Performance PMSM Controller

Implementation of the permanent magnet synchronous motor vector control implies strong time dependencies. The control process requires precise measurement of motor shaft position and winding currents to establish correct driving. The tight time dependencies are difficult to achieve using a programmatic approach. Specific controller architecture is proposed for programmable systems on chip architectures enabling operations precise timing and improved processing performance. The controller is decomposed into a dedicated hardware interface system and programmatic part for easy implementation and modification of the control algorithm. The proposed architecture offers precise and repeatable input-output operations timing and assures meeting tight time dependencies. The control algorithm is executed as an interrupt service requested by the interface system in a constant processing period with relatively weak time dependencies. Additionally, the interface system preprocesses input and output signals reducing the computation effort and saving time for algorithm computations. The specific implementation enabled improved measurement of the motor’s windings current with suppression of disturbances caused by inverter operation. There is shown an efficient implementation of Parke’s and Clarke’s transformations using specific resources of modern programmable logic devices. In opposite to the software-managed implementation presented implementation assures completing processing faster, using a minimal number of hardware resources of the FPGA platform and offering the highest flexibility of software part implementation.

Interferometric evaluation of positioning error and position repeatability on CNCs

The interferometer is widely used for various applications concerning high precision distance and position measurements, especially for the calibration of numerically controlled machines. While the setup procedures of the interferometer may be provided by the manufacturer, some calibration procedures are well defined by the international standards. Since the operation of interferometers requires qualified personnel, some helpful hints for the novice users are to be presented in this paper. Even if the interferometer is highly recommended by international calibration standards, some factors are prone to intervene into the quality of results. This paper presents the experimental results for the evaluation of positioning accuracy and repeatability on Y axis of two vertical machining centres. The results show the high importance of environmental conditions compensation, the impact of time pauses during the measurement procedure and the implications of the increment of measuring target positions.

Deep-SMOLM: deep learning resolves the 3D orientations and 2D positions of overlapping single molecules with optimal nanoscale resolution.

Dipole-spread function (DSF) engineering reshapes the images of a microscope to maximize the sensitivity of measuring the 3D orientations of dipole-like emitters. However, severe Poisson shot noise, overlapping images, and simultaneously fitting high-dimensional information-both orientation and position-greatly complicates image analysis in single-molecule orientation-localization microscopy (SMOLM). Here, we report a deep-learning based estimator, termed Deep-SMOLM, that achieves superior 3D orientation and 2D position measurement precision within 3% of the theoretical limit (3.8° orientation, 0.32 sr wobble angle, and 8.5 nm lateral position using 1000 detected photons). Deep-SMOLM also demonstrates state-of-art estimation performance on overlapping images of emitters, e.g., a 0.95 Jaccard index for emitters separated by 139 nm, corresponding to a 43% image overlap. Deep-SMOLM accurately and precisely reconstructs 5D information of both simulated biological fibers and experimental amyloid fibrils from images containing highly overlapped DSFs at a speed ~10 times faster than iterative estimators.