One-step Calibration Research Articles

Micro bi-prism bi-telecentric single lens Stereo-DIC system using one-step calibration method

In recent years, the bi-prism bi-telecentric single lens stereo digital image correlation (BBSL Stereo-DIC) system has emerged as a viable approach for measuring stereo surface deformation. However, the reliance on a bi-prism that needs to be precisely aligned perpendicular to the optical axis of the bi-telecentric lens using a laser beam, as well as the need to remove the bi-prism during the calibration phase, impose limitations on the practical application of the existing method. To overcome these challenges, we propose a convenient one-step calibration method that eliminates the positional dependence on the bi-prism. This method incorporates the bi-prism’s attitude parameter and principal point coordinates as additional intrinsic parameters. Similar to traditional binocular calibration, the calibration process involves capturing a series of images of a calibration target at various positions and orientations, making it convenient and straightforward for DIC users. A numerical simulation calibration experiment is performed to illustrate the difference between the proposed method and the existing method. The result shows that the bi-prism’s attitude parameter has a significant impact on 3D reconstruction. A rigid-body translation experiment and a tensile experiment of an 800H alloy micro-specimen with a notch are conducted on a micro BBSL Stereo-DIC system. The results and the comparison with finite element simulation prove the accuracy of the proposed method, which demonstrates that the one-step calibration method can be easily employed for micro stereo surface deformation measurement.

Bi-prism-based single-bilateral-telecentric-camera stereo-DIC for accurate underwater 3D deformation measurement: Implementation of a parametric model

Full-field surface shape and deformation measurements of submerged objects using stereo-digital image correlation (stereo-DIC) remains challenging due to the light ray refraction occurred on the interface of two different transparent media (e.g., air, glass and water). In this work, we proposed an underwater full-field 3D deformation measurement method based on the bi-prism-based single-bilateral-telecentric-camera (SBTC) stereo-DIC, which adopts a parametric model to establish the mathematical relationship between the image points and their corresponding object points by taking the refraction into account in the ray-tracing process. The key parameters (e.g., bi-prism/glass orientation and position) of the parametric model were calibrated by a one-step calibration. To verify the correctness and effectiveness of the proposed method, translation tests with a rotated bi-prism and underwater translation tests were performed. Experimental results indicate that the proposed parametric model can effectively handle the imperfect system configuration and the unavoidable light ray refraction that occurred on the optical path, thus allowing high-accuracy underwater deformation measurement. Compared with the existing underwater deformation measurement approaches, the proposed method can not only deliver displacement measurement with higher accuracy, but also is free of any assumptions on the configuration of the camera system or the refractive interface.

Soft Robots' Dynamic Posture Perception Using Kirigami-Inspired Flexible Sensors with Porous Structures and Long Short-Term Memory (LSTM) Neural Networks.

Soft robots can create complicated structures and functions for rehabilitation. The posture perception of soft actuators is critical for performing closed-loop control for a precise location. It is essential to have a sensor with both soft and flexible characteristics that does not affect the movement of a soft actuator. This paper presents a novel end-to-end posture perception method that employs flexible sensors with kirigami-inspired structures and long short-term memory (LSTM) neural networks. The sensors were developed with conductive sponge materials. With one-step calibration from the sensor output, the posture of the soft actuator could be calculated by the LSTM network. The method was validated by attaching the developed sensors to a soft fiber-reinforced bending actuator. The results showed the accuracy of posture prediction of sponge sensors with three kirigami-inspired structures ranged from 0.91 to 0.97 in terms of . The sponge sensors only generated a resistive torque value of 0.96 mNm at the maximum bending position when attached to a soft actuator, which would minimize the effect on actuator movement. The kirigami-inspired flexible sponge sensor could in future enhance soft robotic development.

A practical guide to scanning light-field microscopy with digital adaptive optics.

With the development of a wide variety of animal models in recent years, there is a rapidly growing demand for long-term, high-speed intravital fluorescence imaging to observe intercellular and intracellular interactions in their native states. Scanning light-field microscopy (sLFM) with digital adaptive optics provides a compact computational solution by imaging the entire volume in a tomographic way with orders-of-magnitude improvement in spatiotemporal resolution and reduction in phototoxicity, as compared to traditional intravital microscopy. Here, we present a step-by-step protocol for both hardware and software implementation of multicolor sLFM as an add-on to a normal wide-field fluorescence microscope by using off-the-shelf lenses and devices at low cost. The procedure can be easily applied to other LFM variants, which can be advantageous in certain experimental contexts. Owing to the strong reliance of sLFM on algorithmic post-processing for high-quality data, the protocol describes various kinds of artefacts and corresponding parameters used for correcting and performance optimization. To increase the tolerance to system misalignment and differences in device fabrication, we describe a one-step calibration method for robust imaging performance up to the diffraction limit. An open-source graphical user interface is presented for hardware synchronization and real-time rendering of multiview images. The whole procedure including optical setup, software installation, system calibration and 3D reconstruction can be executed in 3-4 d with basic knowledge in optics and electronics.

The research on pipe structural behavior of 3D UOE manufacturing process

A 3D UOE manufacturing process is established by ABAQUS software in this study with the consideration of detailed boundary conditions. From two aspects of geometric profile and material distribution, the effects of each forming step are determined from three directions: circumferential direction, radial direction and longitudinal direction. As for the geometric profile of the 3D UOE model, the radius distribution of X70 is more concentrate around the nominal value than X80 pipe. As the longitudinal deformation in O forming and expansion step is not uniform, greater compression ratio and expansion ratio are needed for reducing section ovality. Under the effect of twice expansion steps, the ovality in the overlapping area is smaller than that in the region subjected to one-step calibration. As for the structural behavior of UOE pipe, the weakest position of the pipe after UOE manufacturing process is determined according to the principle of Bauschinger effect. Different with 2D model, 3D UOE pipe has a stronger collapse resistance under the effect of low ovality and the supporting of neighboring sections. Comparing with the offshore standard DNV-OS-F101, the accuracy of 3D UOE model is verified whose resistance to the external pressure is more sensitive with the expansion ratio than the internal pressure.

One-Step Calibration of AFM in Liquid

Nanomechanical measurements of cells and single molecules with atomic force microscopy (AFM) require accurate calibration of two parameters: the spring constant of the cantilever (k) and the inverse of the optical lever sensitivity (InvOLS). The most established calibration approach in liquid consists in determining the InvOLS from force–distance curves on a stiff surface, k being calculated using the thermal spectrum (PSD) of the cantilever via the equipartition theorem. Recent works proposed using cantilevers with calibrated k and then determining the InvOLS from the PSD. These non-contact approaches improve the precision of nanomechanical measurements compared to conventional contact-based approaches. The Sader method or the recent global calibration initiative (GCI) are accurate approaches and do not require knowledge of the InvOLS to determine k, thus they would allow one-step calibration of AFM in liquid. However, both methods assume high quality factor cantilevers, not the case for most cantilevers in liquid. Here we assess the accuracy and precision of the Sader and GCI methods in liquid on two types of cantilevers with low Q-factor using two different PSD fitting models (SHO and Pirzer). We evaluate the two approaches using only the PSD in liquid to calibrate both k and the InvOLS. While both methods led to similar results, the GCI approach is less prone to systematic uncertainties and, using the SHO model, provides higher accuracy in k and the InvOLS. Therefore, the proposed SHO, GCI-based approach utilizing only the thermal spectrum in liquid is precise and accurate and allows one-step calibration of AFM.

Dynamic Deformation Measurement of Specular Surface with Deflectometry and Speckle Digital Image Correlation.

The deformation measurement of a specular surface is of great importance during the quality inspection and installation of optical elements or wafers, especially those with large apertures. We propose a deflectometry method with speckle digital image correlation (DeSDIC) to realize the dynamic and high-accuracy measurement of the deformation on specular surfaces, with a simple system structure and robustness to noises and environmental vibrations. Random speckle pattern displayed on liquid crystal display is reflected by the original surface under test (SUT), and the distorted pattern is recorded by a camera. This originally distorted pattern is taken as the reference image, and the patterns captured afterwards are digitally correlated with the reference image to calculate the gradient change and deformation of the SUT. The theoretical relationships and an experimental one-step calibration scheme are proposed. Both static and dynamic deformations of a deformable mirror were experimentally measured to demonstrate the feasibility and accuracy of DeSDIC, which is comparable to phase-measuring deflectometry and interferometry.

Squircle-Based Calibration Algorithm for Six-Port Radar

This article presents a new approach to calibrate six-port radar systems without the need for well-known target positions or calibration standards. Due to an extension of an ellipse-based calibration, the detectors’ nonlinearities can also be included into this one-step calibration. A so-called squircle is used to approximate measured $I/Q$ data of arbitrary and possibly unknown target positions. It is demonstrated with measurement data, that the implicit function of the squircle is suitable to model errors caused by power imbalance, crosstalk or parasitic reflections as well as detector nonlinearities. Furthermore, a method for mapping the impaired measurement data to an ideal circle is presented. This enables the accurate reconstruction of a target’s displacement.

Portable System for Box Volume Measurement Based on Line-Structured Light Vision and Deep Learning.

Portable box volume measurement has always been a popular issue in the intelligent logistic industry. This work presents a portable system for box volume measurement that is based on line-structured light vision and deep learning. This system consists of a novel 2 × 2 laser line grid projector, a sensor, and software modules, with which only two laser-modulated images of boxes are required for volume measurement. For laser-modulated images, a novel end-to-end deep learning model is proposed by using an improved holistically nested edge detection network to extract edges. Furthermore, an automatic one-step calibration method for the line-structured light projector is designed for fast calibration. The experimental results show that the measuring range of our proposed system is 100–1800 mm, with errors less than ±5.0 mm. Theoretical analysis indicates that within the measuring range of the system, the measurement uncertainty of the measuring device is ±0.52 mm to ±4.0 mm, which is consistent with the experimental results. The device size is 140 mm × 35 mm × 35 mm and the weight is 110 g, thus the system is suitable for portable automatic box volume measurement.

Non-orthogonal one-step calibration method for robotized transcranial magnetic stimulation

BackgroundRobotized transcranial magnetic stimulation (TMS) combines the benefits of neuro-navigation with automation and provides a precision brain stimulation method. Since the coil will normally remain unmounted between different clinical uses, hand/eye calibration and coil calibration are required before each experiment. Today, these two steps are still separate: hand/eye calibration is performed using methods proposed by Tsai/Lenz or Floris Ernst, and then the coil calibration is carried out based on the traditional TMS experimental step. The process is complex and time-consuming, and traditional coil calibration using a handheld probe is susceptible to greater calibration error.MethodsA novel one-step calibration method has been developed to confirm hand/eye and coil calibration results by formulating a matrix equation system and estimating its solution. Hand/eye calibration and coil calibration are performed to confirm the pose relationships of the marker/end effector ‘X’, probe/end effector ‘Y’, and robot/world ‘Z’. First, the coil is fixed on the end effector of the robot. During the one-step calibration process, a marker is mounted on the top of the coil and a calibration probe is fixed at the actual effective position of the coil. Next, the robot end effector is moved to a series of random positions ‘A’, the tracking data of marker ‘B’ and probe ‘C’ is obtained correspondingly. Then, a matrix equation system AX = ZB and AY = ZC can be acquired, and it is computed using a least-squares approach. Finally, the calibration probe is removed after calibration, while the marker remains fixed to the coil during the TMS experiment. The methods were evaluated based on simulation data and on experimental data from an optical tracking device. We compared our methods with two classical methods: the QR24 method proposed by Floris Ernst and the handheld coil calibration method.ResultsThe new methods outperform the QR24 method in the aspect of translational accuracy and performs similarly in the aspect of rotational accuracy, the total translational error decreased more than fifty percent. The new approach also outperforms traditional handheld coil calibration of navigated TMS systems, the total translational error decreased three- to fourfold, and the rotational error decreased six- to eightfold. Furthermore, the convergence speed is improved 16- to 27-fold for the new algorithms.ConclusionThese results suggest that the new method can be used for hand/eye and coil calibration of a robotized TMS system. Two complex steps can be simplified using a least-squares approach.

Mirror-based flexible one-step calibration method of light-sectioning system for surface topography.

A flexible, easy-to-implement, one-step calibration method of the light-sectioning system is proposed for surface topography using a mirror adapter. The calibration method employs an arbitrary non-planar object with feature points as a target. With the assistance of the mirror adapter, the real and the reflected images of calibration are spatially separated and captured by a camera. It is developed as a direct calculation (DC) method and a virtual camera (VC) method to optimize the full parameters of the system. The DC method estimates the relative rotation and translation, respectively, and the VC method regards the two images as captured by two cameras in a physical sense through image flipping. The parameters of the laser plane can be solved accordingly. A numerical simulation is performed to analyze the precision of these two methods. A three-dimensional (3D) toy and a mechanical element are measured to verify the validity in translation experiments.

State of charge monitoring of vanadium redox flow batteries using half cell potentials and electrolyte density

The operation of vanadium redox flow batteries requires reliable in situ state of charge (SOC) monitoring. In this study, two SOC estimation approaches for the negative half cell are investigated. First, in situ open circuit potential measurements are combined with Coulomb counting in a one-step calibration of SOC and Nernst potential which doesn't need additional reference SOCs. In-sample and out-of-sample SOCs are estimated and analyzed, estimation errors ≤0.04 are obtained. In the second approach, temperature corrected in situ electrolyte density measurements are used for the first time in vanadium redox flow batteries for SOC estimation. In-sample and out-of-sample SOC estimation errors ≤0.04 demonstrate the feasibility of this approach. Both methods allow recalibration during battery operation. The actual capacity obtained from SOC calibration can be used in a state of health model.

TWO-STEP CAMERA CALIBRATION METHOD DEVELOPED FOR MICRO UAV'S

Abstract. The development of unmanned aerial vehicles (UAVs) and continuous price reduction of unmanned systems attracted us to this research. Professional measuring systems are dozens of times more expensive and often heavier than "amateur", non-metric UAVs. For this reason, we tested the DJI Phantom 2 Vision Plus UAV. Phantom’s smaller mass and velocity can develop less kinetic energy in relation to the professional measurement platforms, which makes it potentially less dangerous for use in populated areas. In this research, we wanted to investigate the ability of such non-metric UAV and find the procedures under which this kind of UAV may be used for the photogrammetric survey. It is important to emphasize that UAV is equipped with an ultra wide-angle camera with 14MP sensor. Calibration of such cameras is a complex process. In the research, a new two-step process is presented and developed, and the results are compared with standard one-step camera calibration procedure. Two-step process involves initially removed distortion on all images, and then uses these images in the phototriangulation with self-calibration. The paper presents statistical indicators which proved that the proposed two-step process is better and more accurate procedure for calibrating those types of cameras than standard one-step calibration. Also, we suggest two-step calibration process as the standard for ultra-wideangle cameras for unmanned aircraft.

TWO-STEP CAMERA CALIBRATION METHOD DEVELOPED FOR MICRO UAV'S

The development of unmanned aerial vehicles (UAVs) and continuous price reduction of unmanned systems attracted us to this research. Professional measuring systems are dozens of times more expensive and often heavier than "amateur", non-metric UAVs. For this reason, we tested the DJI Phantom 2 Vision Plus UAV. Phantom’s smaller mass and velocity can develop less kinetic energy in relation to the professional measurement platforms, which makes it potentially less dangerous for use in populated areas. In this research, we wanted to investigate the ability of such non-metric UAV and find the procedures under which this kind of UAV may be used for the photogrammetric survey. It is important to emphasize that UAV is equipped with an ultra wide-angle camera with 14MP sensor. Calibration of such cameras is a complex process. In the research, a new two-step process is presented and developed, and the results are compared with standard one-step camera calibration procedure. Two-step process involves initially removed distortion on all images, and then uses these images in the phototriangulation with self-calibration. The paper presents statistical indicators which proved that the proposed two-step process is better and more accurate procedure for calibrating those types of cameras than standard one-step calibration. Also, we suggest two-step calibration process as the standard for ultra-wideangle cameras for unmanned aircraft.

One step geometrical calibration method for optical coherence tomography

We present a novel one-step calibration methodology for geometrical distortion correction for optical coherence tomography (OCT). A calibration standard especially designed for OCT is introduced, which consists of an array of inverse pyramidal structures. The use of multiple landmarks situated on four different height levels on the pyramids allow performing a 3D geometrical calibration. The calibration procedure itself is based on a parametric model of the OCT beam propagation. It is validated by experimental results and enables the reduction of systematic errors by more than one order of magnitude. In future, our results can improve OCT image reconstruction and interpretation for medical applications such as real time monitoring of surgery.

ACTRIS non-methane hydrocarbon intercomparison experiment in Europe to support WMO GAW and EMEP observation networks

Abstract. The performance of 18 European institutions involved in long-term non-methane hydrocarbon (NMHC) measurements in ambient air within the framework of the Global Atmosphere Watch (GAW) and the European Monitoring and Evaluation Programme (EMEP) was assessed with respect to data quality objectives (DQOs) of ACTRIS (Aerosols, Clouds, and Trace gases Research InfraStructure Network) and GAW. Compared to previous intercomparison studies the DQOs define a novel approach to assess and ensure a high quality of the measurements. Having already been adopted by GAW, the ACTRIS DQOs are demanding with deviations to a reference value of less than 5 % and a repeatability of better than 2 % for NMHC mole fractions above 0.1 nmol mol−1. The participants of the intercomparison analysed two dry gas mixtures in pressurised cylinders, a 30-component NMHC mixture in nitrogen (NMHC_N2) at approximately 1 nmol mol−1 and a whole air sample (NMHC_air), following a standardised operation procedure including zero- and calibration gas measurements. Furthermore, participants had to report details on their instruments and assess their measurement uncertainties. The NMHCs were analysed either by gas chromatography–flame ionisation detection (GC-FID) or by gas chromatography–mass spectrometry (GC-MS). For the NMHC_N2 measurements, 62 % of the reported values were within the 5 % deviation class corresponding to the ACTRIS DQOs. For NMHC_air, generally more frequent and larger deviations to the assigned values were observed, with 50 % of the reported values within the 5 % deviation class. Important contributors to the poorer performance in NMHC_air compared to NMHC_N2 were a more complex matrix and a larger span of NMHC mole fractions (0.03–2.5 nmol mol−1). The performance of the participating laboratories were affected by the different measurement procedures such as the usage of a two-step vs. a one-step calibration, breakthroughs of C2–C3 hydrocarbons in the focussing trap, blank values in zero-gas measurements (especially for those systems using a Nafion® Dryer), adsorptive losses of aromatic compounds, and insufficient chromatographic separation.

One-step calibration of magnetic gradient tensor system with nonlinear least square method

Due to technological limitations, the accuracy of magnetic gradient tensor system is tightly affected by different scale factors, bias of each axis, non-orthogonality between axes and misalignment errors between magnetometers. In order to obtain precise measurement, calibration of the magnetic gradient tensor system is quite essential. A mathematical model containing error parameters of magnetic gradient tensor system is established, and one-step calibration method based on nonlinear least square method is proposed. The effectiveness and convergence of the proposed algorithm is proved by simulation and experiments. In experiments, a tri-axial nonmagnetic rotation platform, a proton magnetometer and a cross magnetic gradient tensor system containing four three-axis fluxgate magnetometers are used. Experimental results show that the proposed method can decrease the measurement errors of magnetic gradient tensor system greatly.

Developing Calibration Weights and Standard-Error Estimates for a Survey of Drug-Related Emergency-Department Visits

Abstract This article describes a two-step calibration-weighting scheme for a stratified simple random sample of hospital emergency departments. The first step adjusts for unit nonresponse. The second increases the statistical efficiency of most estimators of interest. Both use a measure of emergency-department size and other useful auxiliary variables contained in the sampling frame. Although many survey variables are roughly a linear function of the measure of size, response is better modeled as a function of the log of that measure. Consequently the log of size is a calibration variable in the nonresponse-adjustment step, while the measure of size itself is a calibration variable in the second calibration step. Nonlinear calibration procedures are employed in both steps. We show with 2010 DAWN data that estimating variances as if a one-step calibration weighting routine had been used when there were in fact two steps can, after appropriately adjusting the finite-population correct in some sense, produce standard-error estimates that tend to be slightly conservative.

ONE-STEP AND TWO-STEP CALIBRATION OF A PORTABLE PANORAMIC IMAGE MAPPING SYSTEM

Abstract. A Portable Panoramic Image Mapping System (PPIMS) is proposed for rapid acquisition of three-dimensional spatial information. By considering the convenience of use, cost, weight of equipment, precision, and power supply, the designed PPIMS is equipped with 6 circularly arranged cameras to capture panoramic images and a GPS receiver for positioning. The motivation for this design is to develop a hand-held Mobile Mapping System (MMS) for some difficult accessing areas by vehicle MMS, such as rugged terrains, forest areas, heavily damaged disaster areas, and crowed places etc. This PPIMS is in fact a GPS assisted close-range photogrammetric system. Compared with the traditional close-range photogrammetry, PPIMS can reduce the need of ground control points significantly. Under the condition of knowing the relative geometric relationships of the equipped sensors, the elements of exterior orientation of each captured image can be solved. However, the procedure of a system calibration should be done accurately to determine the relative geometric relationships of multi-cameras and the GPS antenna center, before the PPIMS can be applied for geo-referenced mapping. In this paper, both of one-step and two-step calibration procedures for PPIMS are performed to determine the lever-arm offsets and boresight angles among cameras and GPS. The performance of the one-step and two-step calibration is evaluated through the analysis of the experimental results. The comparison between these two calibration procedures was also conducted. The two-step calibration method outperforms the one-step calibration method in terms of calibration accuracy and operation convenience. We expect that the proposed two-step calibration procedure can also be applied to other platform-based MMSs.

ONE DECADE MICROWAVE FORWARD NETWORK ANALYZER BASED ON THE MULTI-PORT TECHNIQUE

This paper presents a one decade low-cost forward network analyzer based on a modifled six-port technique. An instrumentation integrating the hardware and software resources ofiering advantages such as robustness and compactness is developed. The microwave part of the system is fabricated in planar technology. Associated to this system, a one-step calibration procedure is implemented on an 8-bits microcontroller. The performance, in term of measurement accuracy, is evaluated by comparing the results obtained from the system proposed to those given by a conventional network analyzer in the frequency band 1{10GHz.