Coordinate Measurement System Research Articles

Correction of Over-the-Air Transmit and Receive Wireless Device Performance Errors Due to Displaced Antenna Positions in the Measurement Coordinate System

Over-the-air (OTA) performance evaluation for wireless devices require electromagnetic field measurements in the far-field (FF). This is typically achieved by using one or multiple test probes to scan a sphere encompassing the device under test (DUT), which can be either set to transmit (Tx) or receive (Rx). Measurement data are usually collected in magnitude-only and near-field to FF transformations cannot be straightforwardly applied in a majority of test cases. In the case of large DUT, the active antenna in the device may not be located at the center of the measurement coordinate system, due to mechanical positioner or anechoic chamber constraints. Such an offset is known to introduce significant errors on assessed radiated quantities, which are mostly due to variations in the path length and the angular position of the apparent phase center of the Tx/Rx structure, with respect to the probe boresight direction. This article proposes a novel solution to this problem and introduces an algorithm to compensate errors from known antenna displacements within the coordinate system. This compensation applies to both OTA Tx and Rx cases. The accuracy of the identified solution is demonstrated through simulated and experimental results, using setups operating at 5G NR millimeter-wave frequencies.

Uncertainty assessment of a prototype of multilateration coordinate measurement system

Large Volume Metrology is essential to many high value industries to go towards the factory of the future, but also to many science facilities for fine alignment of large structures. In this context, we have developed a multilateration coordinate measurement system, traceable to SI metre, and suitable for outdoor measurements or industrial environments. It is based on a high accuracy absolute distance meter developed in-house and shared between several measurement heads by fibre-optic links. Thus, from these measurement stations, multiple distance measurements of several positions of a target can be performed. At the end, coordinates of the heads and of the different target locations are determined using a multilateration algorithm with self-calibration.In this paper, the uncertainty of this multilateration coordinate measurement system is determined with a consistent metrological approach. First, 13 different sources of errors are listed and quantified. Then, thanks to Monte Carlo simulations, the standard uncertainty on a single absolute distance measurement is assessed to 4.7 μm. This includes the uncertainty contribution of the telemetric system itself, but also the contributions of the mechanical designs of the measurement heads and the target. Lastly, measurements of three-dimensional coordinates of target positions are performed in a control environment, then in a large workshop without temperature control: these measurements validate the uncertainty assessment of the system.

REFINEMENTS AND INTRODUCTION OF PHOTOGRAMMETRIC ELEMENTS TO AN EXPERIMENTAL TRILATERATION BASED OPTICAL METROLOGY SYSTEM

Abstract. OPTIMUM is a novel optical coordinate measurement system designed to determine the location of omnidirectional targets within a large volume, the previous version of the system could determine the targets location with an uncertainty of 50 × 10−6 m. This paper describes some of the limitations of the original embodiment and changes being developed to address them. Version 2 of the system aims to solve the limitations of version 1 by integrating photogrammetric processes into the design and control processes of the system, along with redesigning the mechanical and optical relationships. The redesigned instrument will result in the ability to fully automate the initial calibration process and to allow for real-time processing of the measurement algorithms.

Construction and uncertainty evaluation of large-scale measurement system of laser trackers in aircraft assembly

A high-accuracy, large-scale measurement system of laser trackers is essential for aircraft assembly. The registration from a measurement coordinate system (MCS) to an assembly coordinate system (ACS) depends on an enhanced reference system (ERS). The usual method to construct a measurement system is the best-fit of single station (BFSS) method, which is highly sensitive to ERS deviation. In this paper, a bundle adjustment of multiple stations (BAMS) method is proposed. First, all the measurement stations and ERS are built into an entire measurement coordinate system (EMCS) through bundle adjustment. Then, stable ERS points are used to register the EMCS to the ACS. An error model of the BAMS is built and the proposed BAMS is demonstrated to have smaller registration parameter errors. Furthermore, the uncertainty of measurement system is evaluated through simulations and experiments, showing that the BAMS constrains the uncertainty considerably better than the BFSS.

Research on the influence of background light on the accuracy of a three-dimensional coordinate measurement system based on dual-PSD

PurposeThe purpose of this paper is to analyze the measurement error of a three-dimensional coordinate measurement system based on dual-position-sensitive detector (PSD) under different background light.Design/methodology/approachThe mind evolutionary algorithm (MEA)-back propagation (BP) neural network is used to predict the three-dimensional coordinates of the points, and the influence of the background light on the measurement accuracy of the three-dimensional coordinates based on PSD is obtained.FindingsThe influence of the background light on the measurement accuracy of the system is quantitatively calculated. The background light has a significant influence on the prediction accuracy of the three-dimensional coordinate measurement system. The optical method, electrical method and photoelectric compensation method are proposed to improve the measurement accuracy.Originality/valueBP neural network based on MEA is applied to the coordinate prediction of the three-dimensional coordinate measurement system based on dual-PSD, and the influence of background light on the measurement accuracy is quantitatively analyzed.

Motion and inertial parameter estimation of non-cooperative target on orbit using stereo vision

In the on-orbit servicing missions, autonomous close proximity operations require knowledge of the target’s motion and inertial parameters in order to safely interact with the target. In particular, the motion and parameter estimation of an uncooperative target is a challenging task because of the lack of some prior information about the target in unfamiliar environments. In this paper, a novel method is developed for an accurate estimation of the motion and inertial parameters of an unknown target using stereo vision measurements only. Instead of using relative position and pose as observation information, this paper chooses three non-collinear feature points on the target as estimation measurements. This treatment allows us to estimate the principal axis of inertia of the target directly, and avoid estimating the quaternion between the target measurement coordinate system and the principal axis of inertia coordinate system, which is a bilinear problem, and is difficult to obtain global convergence. Based on the relative kinematics and dynamics equations of the target, the state equation and observation equation are derived, and the Extended Kalman Filter (EKF) is designed. As a result, the developed algorithm realizes the estimation of the complete unknown information of the target, including relative position, relative velocity, attitude quaternion, angular velocity, the direction of the principal axis of inertia, inertia ratio, and the position of center of mass. Numerical simulations and experimental results verify the convergence and effectiveness of the proposed filter estimation method.

Study on the strategy of 3D images based reconstruction using a camera attached to a robot arm

The metric distance error between the calculated point and the real point in the 3D measurement coordinate system is due to optimization methods carried out in 2D image plane. Euclidian image based 3D reconstruction is carried out in three major steps, geometric primitive extraction, correspondence, and triangulation. Extraction and triangulation are purely geometric tasks but the correspondence step is a challenge in precision. In this paper we study 3D object reconstruction based on a set of 2D images. We used a robot arm to accurately move the camera and we study the influence of the motion. It has been demonstrated that the impact of a correspondence error on the reconstruction accuracy of a 3D images-based reconstructed point may vary depending on the image capture strategy. Two modes of motion have been adopted. The first is an axial mode making the camera close or far from the object acting like a zoom. The second mode is lateral where the camera moves parallel to the object. It has been shown that axial mode leads to greater errors compared to the lateral mode. The impact of the geometric parameters of photographing on images based 3D reconstruction error is also discussed.

Overlap method for the performance evaluation of coordinate measurement systems and the calibration of one-dimensional artifacts

This article describes a method called ‘overlap’ to perform two main tasks. The first is the performance evaluation of a coordinate measurement system (CMS) with a measuring range larger than the length of artifacts. The second is the calibration of one-dimensional artifacts using a CMS with a measuring range smaller than the length of the artifacts. Examples of one-dimensional artifacts are ball bars, step gauges, or scale bars with lines or circle marks. For the first task, the method uses the translation between errors in a line inside the volume of the CMS. For the second task, it uses the rotation and translation between 3D coordinates of elements belonging to the artifact. Validation of the method for the first task is done by evaluating the performance of a coordinate measuring machine (CMM) in parallel lines to two of its axes. For this, we use a step gauge and a ball bar covering the range of the CMM’s lines under evaluation not using overlap. Later, we evaluate the same lines using a segment of the same step gauge and ball bar but this time using overlap. For the second task, the validation is similar; we use a ball bar whose length falls inside the measurement range of a high-accuracy CMM, then the ball bar can be measured in its entire length with the CMM not using overlap and later in segments using overlap.

Iterative alignment of reflector panels for large-scale compact test range in non-metrology environment based on laser tracker

The reflector panel used for a large-scale compact test range (CTR) is usually divided into several sub-panels with appropriate size to be fabricated separately, and then these sub-panels are assembled and aligned for a long period to form a high-precision reflective surface. Toward that end, an iterative alignment system is established to accomplish alignment of reflector panels based on commercial laser tracker and 6-degree-of-freedom adjustment mechanism. The alignment is a very challenging task involving two aspects: coordinate system alignment and measurement uncertainty evaluation, especially in a non-metrology environment. For the former, an alignment method is developed to unify the measurement coordinate system of the system based on iteratively adding and modifying reference points. For the latter, the actual uncertainty model of laser tracker based on a large amount of field measurement data is analyzed and established using statistical analysis. Based on the uncertainty model, the measurement and alignment error is evaluated and verified by Monte Carlo simulations. As verification, 15 sub-panels of the CTR reflector with 12 m width and 7 m height are opportunely assembled and aligned using the iterative alignment system and algorithm. The final root-mean-square error of the deviation between the actual and theoretical profiles is achieved at 0.041 mm, where the accuracy loss caused by alignment is only 7.9% of the theoretical value. Results show that the alignment system and method proposed in this paper is effective and efficient to align the reflector panels for large-scale CTR in a non-metrology environment.

Prediction of three-dimensional coordinate measurement of space points based on BP neural network

In order to improve the measurement accuracy of three-dimensional coordinate measurement system based on dual-PSD, this paper proposes a three-dimensional coordinate measurement method based on back propagation (BP) neural network considering the high ability of the neural network to deal with the complex nonlinear mapping problem. This method can describe the mapping relationship between three-dimensional coordinates of space points in the world coordinate system and coordinates of light spots on dual-PSD well. Levenberg-Marquardt learning algorithm is used to train the network, and then trained BP neural network model is used to predict three-dimensional coordinates of space points. Experimental results show that the average measurement error of space points obtained by the method is low. It proves that the built BP neural network model can be used to predict three-dimensional coordinates of space points. [Submitted 9 July 2018; Accepted 30 October 2018]

A multi-node synchronous baseline calibration system based on vision measurement for DPOS

A distributed position and orientation system (DPOS) can provide abundant time-spatial information for multi-task imaging loads in the airborne earth observation system. To ensure that DPOS meets the engineering requirement, it must be accurately calibrated on the ground before DPOS can be applied to aerial remote sensing, especially baseline calibration, for which the measurement accuracy of the baseline is a key technical indicator that affects imaging accuracy. However, it is difficult to achieve baseline calibration between multiple nodes synchronously because of external interference, and there is no baseline calibration method for DPOS yet. To solve the problem mentioned above, considering the advantages of vision measurement, this paper presents a multi-node synchronous baseline calibration system for DPOS. In order to evaluate the effectiveness of the proposed system, a verification test was conducted. The measurement result of a theodolite coordinate measurement system (TCMS) is the benchmark. Under static conditions, the experimental results show that baseline measurement accuracy is better than 0.3 mm.

FDnCNN-based image denoising for multi-labfel localization measurement

Recently, the discriminant learning denoising model has deserved special attention due to its outstanding denoising property. This paper designs the RFID multi-label dynamic localization system based on visual measurement to avoid electromagnetic interference. Firstly, the potential sharp images are estimated via denoising images acquired by dual CCD. Then the labels are matched by template. Finally, Shaft Alignment Method (SAM) models the multi-label 3D coordinates in world space and image pixel. Flexible Feed-forward Denoising Convolutional Neural Network (FDnCNN) is proposed to reach the equilibrium between denoising effect and image particulars without producing artifacts in GPU effectively and flexibly. FDnCNN increases the image quality by at least 0.5 dB than WNNM and DnCNN. The 3D coordinate measurement system is evaluated by error, which proves the feasibility and effectiveness of the positioning system.

Prediksi Model 2d Data Magnetotelurik Terbaik Berdasarkan Pendekatan Model Irisan Di Cekungan Tomori dan Sekitarnya

2D modeling of magnetotelluric data produce various models that are influenced by noise and differences in coordinate measurement systems with strike directions, so the results are inaccurate. A technique that can be done to identify the accuracy of the data is the rotation analysis based on the overlay model approach. The type of rotation used are strike angle and fix angle. The strike angle rotation is done by maximizing the anti-diagonal impedance value, while the rotation fix angle refers to the isotropic homogeneous earth model by eliminating the static effect on the surface. The overlay model approach is based on the assumption that the distribution of resistivity variations of the rock in the subsurface has same value in various models. 2D modeling used in this analysis consists of three trajectories of correlation results from 30 magnetotelluric measurement points in the Tomori and surrounding areas. The results of the analysis show that the strike angle rotation model is the best model that can be used in the study area with the approach of determination value reaches 0.7735, therefore it can reduce subsurface geological interpretation deviation based on various 2D models.Keywords: Magnetotelluric, impedance rotation, strike angle rotation, fix angle rotation

Prediksi Model 2d Data Magnetotelurik Terbaik Berdasarkan Pendekatan Model Irisan Di Cekungan Tomori dan Sekitarnya

2D modeling of magnetotelluric data produce various models that are influenced by noise and differences in coordinate measurement systems with strike directions, so the results are inaccurate. A technique that can be done to identify the accuracy of the data is the rotation analysis based on the overlay model approach. The type of rotation used are strike angle and fix angle. The strike angle rotation is done by maximizing the anti-diagonal impedance value, while the rotation fix angle refers to the isotropic homogeneous earth model by eliminating the static effect on the surface. The overlay model approach is based on the assumption that the distribution of resistivity variations of the rock in the subsurface has same value in various models. 2D modeling used in this analysis consists of three trajectories of correlation results from 30 magnetotelluric measurement points in the Tomori and surrounding areas. The results of the analysis show that the strike angle rotation model is the best model that can be used in the study area with the approach of determination value reaches 0.7735, therefore it can reduce subsurface geological interpretation deviation based on various 2D models.Keywords: Magnetotelluric, impedance rotation, strike angle rotation, fix angle rotation

Pose error correction in offline three-dimensional profile measurement system for large-diameter aspheric mirror.

This paper proposes an offline measurement method for a large aspheric mirror during its grinding stage. A measurement method and mathematical model to realize a three-dimensional (3D) profile measurement for large-diameter aspheric mirrors are proposed, based on a cylindrical coordinate system. The measurement error induced by the alignment error is examined based on the error analysis of the measurement and workpiece coordinate systems. The corresponding pose error obtained through the nonlinear least squares method is eliminated to improve the measurement accuracy. To evaluate the entire surface profile error, a 3D profile model is established. The total uncertainties of the proposed measurement system are also estimated. Comparison experiments for a 300-mm-diameter K9 glass workpiece are conducted on UPFM900 and Taylor Hobson PGI 3D profile instruments, and the profile accuracy is found to be improved from 15.3 to 7.12μm after eccentricity and tilt error elimination.

Characterization of the effects of detector angular misalignments and accuracy enhancement of X-ray CT dimensional measurements

Characterization of the effects of detector angular misalignments and accuracy enhancement of X-ray CT dimensional measurements

Femoral morphology asymmetry in hip dysplasia makes radiological leg length measurement inaccurate.

The aim of this study was to examine whether hips with unilateral osteoarthritis (OA) secondary to developmental dysplasia of the hip (DDH) have significant asymmetry in femoral length, and to determine potential related factors. We enrolled 90 patients (82 female, eight male) with DDH showing unilateral OA changes, and 43 healthy volunteers (26 female, 17 male) as controls. The mean age was 61.8 years (39 to 93) for the DDH groups, and 71.2 years (57 to 84) for the control group. Using a CT-based coordinate measurement system, we evaluated the following vertical distances: top of the greater trochanter to the knee centre (femoral length GT), most medial prominence of the lesser trochanter to the knee centre (femoral length LT), and top of the greater trochanter to the medial prominence of the lesser trochanter (intertrochanteric distance), along with assessments of femoral neck anteversion and neck shaft angle. The percentages of hips with an absolute difference of > 5 mm in femoral GT and LT lengths were significantly larger in the DDH group (24% for both) compared with those of the control group (2% and 7%, respectively). The femoral length GT of the affected femur was significantly shorter in Crowe I and longer in Crowe IV than that of the unaffected side. The affected-to-unaffected difference of the intertrochanteric distance showed positive correlation with that of the femoral length GT in Crowe I and Crowe II/III, and negative correlation with that of the femoral length LT in the Crowe I and Crowe IV groups. Hips with unilateral end-stage OA secondary to DDH show significant asymmetry in femoral length between both the greater and lesser trochanter and the knee compared with controls. The intertrochanteric distance was a morphological factor related to femoral-length asymmetry. When undertaking total hip arthroplasty (THA) in the presence of DDH, long leg radiographs or CT measurements should be used to assess true leg-length discrepancy. Cite this article: Bone Joint J 2019;101-B:297-302.

Calibration and uncertainty estimation of non-contact coordinate measurement systems based on Kriging models

Non-contact three dimensional (3D) coordinate measurement systems (CMSs) using optical scanning techniques have the advantage of fast acquiring large numbers of points. However, these systems are known to be less accurate in comparison to the contact-based counterparts. To improve the measurement accuracy of non-contact 3D CMSs, a novel Kriging models-based calibration and uncertainly estimation method is proposed. The spatial correlation of measurement uncertainty is investigated and the calibration values for unmeasured points based on Kriging models are estimated. A procedure of best model selection is presented, and the influence of the calibration model parameters is analyzed. The proposed calibration method is validated through an ATOS II triple scan system. The results show that a significant accurate improvement for the non-contact 3D measurement system is achieved.

Measurement method of Wolter-I type mandrel based on a contact-type profilometer

Contraposing the surface quality testing of a Wolter-I type mandrel after ultraprecise turning, we propose a measuring method based on a contact-type profilometer and fabricate an adjusting device to assist in measurements. By coordinating probe translational motion in the Z and Y directions, this device provides 6 degrees of freedom. Extracting the feature point on the curve of a meridian section contour, the measurement data of the two aspherical surfaces that constitute a Wolter-I type mandrel can be segregated. This feature point is used as a reference point to make the measurement coordinate and machine coordinate systems coincide with each other in order to calculate the dimensional errors of the mandrel. By choosing samples of different lengths, some property indexes of the mandrel surface, such as roughness, waviness, and form error, can be extracted from the contour error signals via the wavelet transform method. This proposed method can solve the problem that the aspheric surface dimension error and contour form error of the Wolter-I mandrel surface cannot be measured by the profilometer when the aspheric reference vertex cannot be determined. Using this method, only one measuring instrument is required to evaluate the mandrel after diamond turning, which can improve the measurement efficiency, and cover the full spatial wavelength range from the figure error to the surface roughness. In addition, this method has the potential to achieve the in situ measurement of the surface of the Wolter-I type ultra-precision mandrel.

Potential of Workshop Measurement Positioning System to Measure Oscillation Frequencies of Rigid Structures

A workshop measuring and positioning system (wMPS) is a large three-dimensional (3D) coordinate-measurement system based on optoelectronic scanning. It is capable of large-range coverage, high measurement accuracy and frequency, and multi-task synchronous measurement. Existing geodetic instruments cannot measure the intrinsic parameters of strong rigid structures. Thus, this study conducted experiments to explore the feasibility of the wMPS to measure the intrinsic parameters of rigid structures. A test bed was established using a reverse-engineering method to simulate the oscillation frequency of the structure. Displacement data, which changed with the time series through the fast Fourier transformation method, were analyzed to determine the feasibility and range of the wMPS in measuring intrinsic parameters of the structure. The experimental results demonstrated that the wMPS can measure the vibrational frequency up to 9 Hz with a 3-mm amplitude and up to 4 Hz with a 30-mm amplitude.