Vision Measurement System Research Articles

Visual level measurement system application in the technological process automated control system of the recuperative furnace bath

The paper considers the melted material level determining problem in the recuperative furnace bath melter in technological process automated control system for the basalt mineral fiber production. To solve this problem, it is proposed to use a visual level measurement system based on the analysis and processing of the melt boundary image. A block diagram of the visual level measurement system developed by the authors is presented, and an algorithm for determining the melt level using a modified Sobel edge detection method is proposed.

A Monocular Vision Relative Displacement Measurement Method Based on Bundle Adjustment Optimization and Quadratic Function Correction

In order to meet the requirements of high-precision target displacement measurement, this paper proposed a measurement method based on monocular vision measurement system by which the advantages of simple structure, convenient debugging, easy to install and calibrate is recognized. This method first uses the bundle adjustment algorithm with conditional constraints to optimize the solution results of the orthogonal iterative algorithm, then calculates the relative poses of the optimization results, finally establishes an error correction model to perform secondary optimization on the relative poses. The experimental results show that the method proposed in this paper can reduce more than 54% average error of displacement measurement results, and the error between the final displacement measurement results and the actual displacement values is controlled at 0.4mm level, which proves that the method has good practical value.

A novel vision measurement system for health monitoring of tunnel structures

Automation and intelligent health monitoring technologies will be one of the most important development directions for rail transit operation and maintenance considering the continuous expansion of the scale of urban rail transit and the increase of labor costs. The highly accurate, full-field data acquisition based on vision measurement technology, which is combined with photogrammetry and three-dimensional scanning technology, is an effective way to improve the intelligence of monitoring. In this paper, accuracy tests of vision measurement and total station technology in multipoint measurement is carried out under the same conditions where the accuracy and reliability are compared according to the various datasets which are collected from experiment and testing. A novel visual measurement technology is proposed for the deformation monitoring of tunnel structures, such as settlement and convergence. The results show that the measurement system has a resolution of 0.01 mm which is better than the total station resolution, and the deviation ratios of the vertical and horizontal displacement are 1.6% and 2.5%, which demonstrate the proposed system has a good potential for practical applications in terms of resolution and accuracy.

An improved particle filtering to locate the crop boundary of an unharvested region using vision

PurposeAccurately, positioning is a fundamental requirement for vision measurement systems. The calculation of the harvesting width can not only help farmers adjust the direction of the intelligent harvesting robot in time but also provide data support for future unmanned vehicles.Design/methodology/approachTo make the length of each pixel equal, the image is restored to the aerial view in the world coordinate system. To solve the problem of too much calculation caused by too many particles, a certain number of particles are scattered near the crop boundary and the distribution regularities of particles’ weight are analyzed. Based on the analysis, a novel boundary positioning method is presented. In the meantime, to improve the robustness of the algorithm, the back-projection algorithm is also used for boundary positioning.FindingsExperiments demonstrate that the proposed method could well meet the precision and real-time requirements with the measurement error within 55 mm.Originality/valueIn visual target tracking, using particle filtering, a rectangular is used to track the target and cannot obtain the boundary information. This paper studied the distribution of the particle set near the crop boundary and proposed an improved particle filtering algorithm. In the algorithm, a small amount of particles is used to determine the crop boundary and accurate positioning of the crop boundary is realized.

3D reconstruction of line-structured light based on binocular vision calibration rotary axis.

High-precision 3D topography measurement is essential to ensure quality and performance of shaft parts. Generally, the main difficulty of measuring rotary objects on a turntable is the low accuracy of axis calibration. To solve this problem, this study introduces two methods for calibrating the rotation axis of the turntable and proposes a method for reconstructing the 3D shape of the object by converting the rotation axis parameters of the binocular vision. A calibration camera is used to shoot a 2D checkerboard calibration board against the rotating table, and the calibration process of a high-precision space rotation axis is developed and implemented. This laser vision measurement system consists of a calibration camera, a measurement camera, and a rotation system. This system can realize reconstruction of the 3D shape of the object in accordance with the rotation axis parameters in any position. The experiment on measuring standard parts verifies the effectiveness of the algorithm. It provides a new idea for the measurement of rotary object shapes.

Validation of an automated‐ETDRS near and intermediate visual acuity measurement

BackgroundThe aim of this study was to determine the repeatability of an automated‐ETDRS (Early Treatment Diabetic Retinopathy Study) near and intermediate visual acuity measurement in subjects with normal visual acuity and subjects with reduced visual acuity. The agreement of automated‐ETDRS with gold standard chart‐based visual acuity measurement was also studied.MethodsFifty‐one subjects were tested (aged 23 to 91-years; 33 subjects with normal visual acuity: 6/7.5 or better; 18 subjects with reduced visual acuity: 6/9 to 6/30). Near and intermediate visual acuity of one eye from each subject was measured with an automated tablet‐computer system (M&S Technologies, Inc.) and Precision Vision paper chart in a random sequence. Subjects were retested one week later. Repeatability was evaluated using the 95 per cent limits of agreement (LoA) between the two visits.ResultsAverage difference between automated‐ETDRS near visual acuity and near visual acuity by paper chart was 0.02 ± 0.10 logMAR (p > 0.05). Agreement of near visual acuity between automated‐ETDRS and paper chart was good, with 95 per cent LoA of ±0.19 logMAR. Furthermore, automated‐ETDRS near visual acuity showed good repeatability (95 per cent LoA of ±0.20). Mean difference between automated‐ETDRS intermediate visual acuity and intermediate visual acuity by paper chart was 0.02 ± 0.10 logMAR (p > 0.05). Agreement of intermediate visual acuity between automated‐ETDRS and paper chart was good, with 95 per cent LoA of ±0.20 logMAR. In addition, automated‐ETDRS intermediate visual acuity had good repeatability (95 per cent LoA of ±0.16).ConclusionAutomated‐ETDRS near and intermediate visual acuity measurement showed good repeatability and agreement with the gold standard chart‐based visual acuity measurement. The findings of this study indicate the automated visual acuity measurement system may have potential for use in both patient care and clinical trials.

Accurate Calibration for Large-Scale Tracking-Based Visual Measurement System

The combination of a large-field-of-view visual positioning system and a local scanning sensor affords an effective approach to the 3-D measurement of meter-scale objects and has been actively investigated by researchers. The calibration of such an integrated measurement system is essential to establish the overall measurement accuracy. This article proposes to calculate the transformation relationship between the local system and the transfer target through the determination of the scales of the combined system. The principle and implementation of this tracking-based combined measurement system are described in this article, as well as the use of the respective scales of the combined system to establish a model of the applicable geometrical relationships. The Kronecker product was used to solve the model equations, after which homogenous transformation matrix optimization was performed. An error model of the camera-based measurement system was also established based on a combination of the image distortion and the working volume. The 2-D and 3-D errors of the local and global sensors were further quantitatively simulated and visualized to demonstrate the calibration accuracy. Standard plane and complex large object measurement experiments were performed to verify the accuracy of the proposed measurement system and its use for the reconstruction of a large shape.

ON-SITE GEOMETRIC CALIBRATION OF THERMAL AND OPTICAL SENSORS FOR UAS PHOTOGRAMMETRY

Abstract. UAS imagery has become a widely used source of information in geomorphic research. When photogrammetric methods are applied to quantify geomorphic change, camera calibration is essential to ensure accuracy of the image measurements. Insufficient self-calibration based on survey data can induce systematic errors that can cause DEM deformations. The typically low geometric stability of consumer grade sensors necessitates in-situ calibration, as the reliability of a lab based calibration can be affected by transport. In this research a robust on-site workflow is proposed that allows the time-efficient and repeatable calibration of thermal and optical sensors at the same time. A stone building was utilised as calibration object with TLS scans for reference. The approach was applied to calculate eight separate camera calibrations using two sensors (DJI Phantom 4 Pro and Workswell WIRIS pro), two software solutions (Vision Measurement System (VMS) and Agisoft Metashape) and two different subsets of images per sensor. The presented results demonstrate that the approach is suitable to determine camera parameters for pre-calibrating photogrammetric surveys.

Camera calibration with global LBP-coded phase-shifting wedge grating arrays

Non-contact optical measurement methods have been widely used in the fields of three-dimensional (3D) machine vision and photogrammetry attributed to their advantages of high precision, high speed and low cost. The calibration results directly affect the accuracy of the vision measurement system. Most of the existing calibration methods with two-dimensional (2D) targets need all of the feature points to be captured by the camera, otherwise it would be difficult to distinguish them due to the usage of identical feature points. This paper presents an active calibration target that consists of phase-shifting wedge gratings (PWGs) with three different periods and globally coded on the basis of rotation invariant local binary pattern (LBP) coding. Feature points are the intersections of several straight lines fitted by the 0 and π phase points. The sub-pixel coordinates can be accurately obtained with the phase-shifting method and the windowed linear fitting. Each feature point has its corresponding label to determine its specific position, therefore the one-to-one correspondence between the image coordinates and world coordinates can be obtained even the images are partially captured, and this characteristic can expand the flexibility in both monocular and multi-camera calibrations. In addition, owing to the phase-shifting method, calibration can be accomplished when the camera is defocused. Simulations and experiments further prove the flexibility and robustness of the proposed method.

Visual measurement system for three dimensional rotation attitudes of the air float turntable

A visual method for 3D attitude measurement of air float turntable based on space vector is proposed. By installing a laser pointer on the surface of the air float turntable, the projection line and the reference plane generate intersection points (light spots) to construct feature points, and use a high-speed camera to achieve the spot’s displacement at different times, the three-dimensional attitude of the air float turntable can be calculated at any time. The turntable’s rotation attitudes are measured by projection method, and the measurement baseline is increased to avoid the adverse influence on the measurement result caused by the nearer feature points distance. A global calibration of the world coordinates for the measurement model is performed to construct an attitudes measurement system. The experimental results show that the measurement system does not affect the functions of other systems on the air float turntable. Adopt 2 mm step calibration in the 2 m × 4 m field of view, the spots’ positioning accuracy is better than 0.09 mm. The maximum standard error of the centroid extraction is 0.0095 pixels, the field of view range is up to ±15°, the yaw angle error is better than ±1.2′, the pitch angle is better than ±1.8′, and the roll angle error is better than 0.42′. The attitude’s information can be transmitted in real time via UDP communication. The results show that the wide-field attitude angle visual measurement system is designed reasonably and can meet high-precision real-time measurement requirements.

PAIN AND AUTONOMY LEVEL OF THE ELDERLY WITH KNEE OSTEOARTHRITIS IN CENTRAL ANATOLIA

Purpose: The aim of this study was to determine the pain and autonomy levels of the elderly with knee osteoarthritis. Materials and Methods: The descriptive study was conducted with 147 patients who consulted the Physiotherapy and Rehabilitation-Orthopedics Clinic of a Research and Application Hospital in a city center The data were obtained by using information form, visual analog scale and functional autonomy measurement system. Results: A significant, moderate negative relationship was observed between the age variable, the sub-dimension of the scale and the Functional Autonomy Measurement System. When the autonomy level of the patients with knee osteoarthritis was evaluated, it was seen that the participants in the 65-74 age group had 1.28 times better autonomy levels compared to those in the 75 and above age group. The study revealed a significant, weak negative relationship between the duration of the illness and daily activities, mental functions and functional autonomy measurement system score averages. Conclusion: It was found that the elderly with knee osteoarthritis have lower levels of autonomy and being single, low education level, advanced age, and increased duration of illness affecting the level of autonomy.

Experimental measurement of fluid flow in high-speed GMAW assisted by transverse magnetic field

Abstract The visual measurement system was established to investigate the fluid flow during high-speed gas metal arc welding. The two-dimensional fluid flow velocity on weld pool surface was measured using the tracer particles. The characteristic parameters of the backward liquid metal flow were extracted, then the speed of the liquid metal flow was compared with different welding speeds. The results showed that the high-speed backward liquid metal flow and the pinching & earlier solidification of the backward liquid metal flow channel caused the humping bead formation. A transverse magnetic field was used to control the fluid flow behavior to prevent the humping bead. Due to the introduction of transverse magnetic field, the thickness of liquid metal layer underneath the arc was increased. The longitudinal velocity of the liquid metal flow was decreased while the transverse velocity was increased so the humping bead can be suppressed.

Accuracy Improvement of Binocular Vision Measurement System for Slope Deformation Monitoring.

This paper studies the limitations of binocular vision technology in monitoring accuracy. The factors affecting the surface displacement monitoring of the slope are analyzed mainly from system structure parameters and environment parameters. Based on the error analysis theory, the functional relationship between the structure parameters and the monitoring error is studied. The error distribution curve is obtained through laboratory testing and sensitivity analysis, and parameter selection criteria are proposed. Corresponding image optimization methods are designed according to the error distribution curve of the environment parameters, and a large number of tests proved that the methods effectively improved the measurement accuracy of slope deformation monitoring. Finally, the reliability and accuracy of the proposed system and method are verified by displacement measurement of a slope on site.

Research on pose estimation for stereo vision measurement system by an improved method: uncertainty weighted stereopsis pose solution method based on projection vector.

We present UWSPSM, an algorithm of uncertainty weighted stereopsis pose solution method based on the projection vector which to solve the problem of pose estimation for stereo vision measurement system based on feature points. Firstly, we use a covariance matrix to represent the direction uncertainty of feature points, and utilize projection matrix to integrate the direction uncertainty of feature points into stereo-vision pose estimation. Then, the optimal translation vector is solved based on the projection vector of feature points, as well the depth is updated by the projection vector of feature points. In the absolute azimuth solution stage, the singular value decomposition algorithm is used to calculate the relative attitude matrix, and the above two stages are iteratively performed until the result converges. Finally, the convergence of the proposed algorithm is proved, from the theoretical point of view, by the global convergence theorem. Expanded into stereo-vision, the fixed relationship constraint between cameras is introduced into the stereoscopic pose estimation, so that only one pose parameter of the two images captured is optimized in the iterative process, and the two cameras are better bound as a camera, it can improve accuracy and efficiency while enhancing measurement reliability. The experimental results show that the proposed pose estimation algorithm can converge quickly, has high-precision and good robustness, and can tolerate different degrees of error uncertainty. So, it has useful practical application prospects.

Binocular stereo vision calibration based on constrained sparse beam adjustment algorithm

In order to realize high-precision three-dimensional measurement of railway train head, a high-precision camera calibration algorithm for binocular stereo vision system based on constrained sparse beam adjustment is proposed in this paper. By analyzing the digital model of binocular vision and the principle of three-dimensional measurement, a binocular stereo vision measurement system based on time-domain coding is built. The edge preservation filtering algorithm based on mean square deviation is used to denoise and filter the visual image. The image is enhanced by histogram equalization. A FAST algorithm based on accelerated segmentation detection is proposed to extract feature information. To solve the problem of camera calibration, a binocular vision calibration method based on coplanar intersecting circle is proposed. The coordinates of circular points are calculated by using the extracted elliptic contour of the intersecting circle, and then the internal parameters of the two cameras and the position relationship between them are obtained. The calibration algorithm needs no manual intervention and has high accuracy. Aiming at the distortion correction, the camera calibration is transformed into a global optimization problem, and the sparse beam adjustment algorithm based on constraints is used to optimize the parameters. Compared with Zhang's calibration method, the results show that the average absolute relative error of the parameters in the two cameras is less than 3.45e−6, the average re-projection error is about 0.1 pixels, and the data accuracy is high, which proves the feasibility and theoretical correctness of the experimental method of the system.

The real-time visual measurement system of rail creeping of high-speed railway

Changes in temperature and stress will lead to the rail creeping of high-speed railway, which becomes a hidden danger in the operation of trains. This paper studies a real-time visual measurement system for creeping displacement monitoring. The bilateral line extraction to determine the target location overcomes the influence of ambient light on image grayscale. The dynamic region of interest setting method is produced to lock and track the target. The self-calibration technology makes the system suitable for field application. The remote transmission of monitoring data is realized through narrow band internet of things (NB-IOT). These methods solve the problems in practical application. The monitoring system provides a reliable guarantee for the safe and stable operation of high-speed railway.

Improved separated-parameter calibration method for binocular vision measurements with a large field of view.

Large field-of-view (FOV) calibration is indispensable to ensure the accuracy of vision measurement systems for large aviation components. We propose an improved separated-parameter calibration method for large-FOV binocular vision measurements with a high flexibility and accuracy. Firstly, the camera parameters are separately calibrated according to the sub-area features of image. Subsequently, based on the spatial-calibration accuracy, a stereoscopic calibration object is devised. The mean error of the proposed method is experimentally obtained as 0.13 mm for a FOV of 2.0 m × 1.5 m. Its feasibility and effectiveness for the measurement in the field is validated by workshop calibration.

Development of a predictive model for kerf taper angle in AWJM of Kevlar epoxy composite

This paper describes the research work involved in studying the influence of process parameters on kerf taper and development of predicative model for the response in abrasive water jet machining (AWJM) of Kevlar epoxy composite. Four process parameters namely water pressure, stand-off distance, traverse speed and abrasive mass flow rate are considered. To investigate the influence of process parameters on kerf taper, experiments are designed using response surface methodology. Experiments are conducted on flying arm AWJM setup. Kerf taper of machined work pieces is measured using vision measurement system. It is found that water pressure and traverse speed are most significant process parameters influencing kerf taper angle. Based on the analysis, a predictive model is developed to predict kerf taper angle. The confirmation tests are performed to verify the predicative model. The findings of present work is useful in minimizing the kerf taper during AWJM of composite materials.

Calibration error compensation technique of stereoscopic vision measurement system

Calibration error compensation technique of stereoscopic vision measurement system

电子元器件外形尺寸机器视觉测量系统设计

电子元器件外形尺寸机器视觉测量系统设计