A conoscopic holography-based 3D measurement system for analyzing defects in steel plate surface

A conoscopic holography-based 3D measurement system for analyzing the defects on the surface of steel plates was introduced in this paper. The hardware, which is automated through software, performs sampling of the steel plate surface. Through the software interface,point-cloud data of the steel plate surface are obtained and reconstructed to form a 3D image of the steel plate surface. The software allows automatic analysis of steel plate surface detects through identification of the bulges and depressions. In addition, the software can also automatically calculate the defect information ,such as the deepest point, volume, opening area, opening length, and so on, thereby determining the defect size. The results determined by this 3D measurement system were found to be in good agreement with the actual values.

Phase unwrapping based on deep learning in light field fringe projection 3D measurement

Phase unwrapping is one of the key roles in fringe projection three-dimensional(3D)measurement technology.We propose a new method to achieve phase unwrapping in camera array light filed fringe projection 3D measurement based on deep learning.A multi-stream convolutional neural network(CNN)is proposed to learn the mapping relationship between camera array light filed wrapped phases and fringe orders of the expected central view,and is used to predict the fringe order to achieve the phase unwrapping.Experiments are performed on the light field fringe projection data generated by the simulated camera array fringe projection measurement system in Blender and by the experimental 3×3 camera array light field fringe projection system.The performance of the proposed network with light field wrapped phases using multiple directions as network input data is studied,and the advantages of phase unwrapping based on deep learning in light filed fringe projection are demonstrated.

An Improved Calibration Method of Grating Projection Measurement System

In the traditional fringe projection profilometry system,the projector and the camera light center are both spatially virtual points.The spatial position relationships specified in the model are not easy to obtain,leading to inaccurate system parameters and affectingmeasurement accuracy.This paper proposes a method for solving the system parameters of the fringe projection profilometry system,and the spatial position of the camera and projector can be adjusted in accordance with the obtained calibration parameters.The steps are as follows:First,in accordance with the conversion relationship of the coordinate system in the calibration process,the calculation formula of the vertical distance from the camera light center to the reference plane and the calculation formula of the distance between the projector and the camera light center are given respectively.Secondly,according to the projector calibration principle,the position of the projector light axis perpendicular to the reference plane is gained by comparing the parallel relationship between the reference plane coordinate system and the projector coordinate system’s Z-axis.Then,in order to fulfill the position restriction that the line between the projector light center and the camera light center must be parallel to the reference plane,the camera’s spatial location is adjusted so that the vertical distance between it and the reference plane tends to that between the projector light center and the reference plane.And finally,the three-dimensional(3D)reconstruction of the target object can be finished using the phase height model’s system parameters once the aforementioned position limitations are put into practice.Experimental results demonstrate that the method improves the measurement accuracy,and verifies that it is effective and available in 3D shape measurement.

MULTIPARAMETER MEASUREMENT FOR RACEWAY GROOVE OF BEARING BASED ON 3D RECONSTRUCTION WITH DIGITAL STRUCTURED LIGHT

A fast 3D reconstruction method based on structured light to measure various parameters of the raceway groove is presented. Digital parallel grating stripes distributed with sine density are projected onto the raceway groove by a DLP projector, and distorting of stripes is happened on the raceway. Simultaneously, aided by three-step phase-shifting approach, three images covered by different stripes are obtained by a high-resolution CCD camera at the same location, thus a more accuracy local topography can be obtained. And then the bearing is rotated on a high precision computer controlled rotational stage. Three images are also obtained as the former step at next planned location triggered by the motor. After one cycle, all images information is combined through the mosaics. As a result, the 3D information of raceway groove can be gained. Not only geometric properties but also surface flaws can be extracted by software. A preliminary hardware system has been built, with which some geometric parameters have been extracted from reconstructed local topography.

Accurate 3D geometry measurement for non-cooperative spacecraft with an unfocused light-field camera

This work explores an alternative 3D geometry measurement method for non-cooperative spacecraft guiding navigation and proximity operations.From one snapshot of an unfocused light-field camera, the 3D point cloud of a non-cooperative spacecraft can be calculated from sub-aperture images with the epipolar plane image(EPI) based light-field rendering algorithm.A Chang'e-3 model(7.2 cm×5.6 cm×7.0 cm) is tested to validate the proposed technique.Three measurement distances(1.0 m, 1.2 m, 1.5 m) are considered to simulate different approaching stages.Measuring errors are quantified by comparing the light-field camera data with a high precision commercial laser scanner.The mean error distance for the three cases are 0.837 mm, 0.743 mm, and 0.973 mm respectively, indicating that the method can well reconstruct 3D geometry of a non-cooperative spacecraft with a densely distributed 3D point cloud and is thus promising in space-related missions.

THEORETICAL ANALYSIS OF COORDINATES MEASUREMENT BY FLEXIBLE 3D MEASURING SYSTEM

The system mathematical model of flexible 3D measuring system is built by theoretical analysis, and the theoretical formula for measuring space point coordinate is also derived. Frog-jumping based coordinate transform method is put forward in order to solve measuring problem for large size parts. The frog-jumping method is discussed, and the coordinate transform mathematical model is method of the space point coordinate compared to original value, and an advanced method is provided, Form the space point coordinate transform formula can derive the calculation measuring method for measuring large size parts.

New Approach for 3D Shape Measurement Based on Color-Coded Fringe and Neural Network

A new 3D surface contouring and ranging system based on digital fringe projection and phase shifting technique is presented. Using the phase-shift technique, points cloud with high spatial resolution and limited accuracy can be generated. Stereo-pair images obtained from two cameras can be used to compute 3D world coordinates of a point using traditional active triangulation approach, yet the camera calibration is crucial. Neural network is a well-known approach to approximate a nonlinear system without an explicit physical model, in this work it is used to train the stereo vision application system to calculating 3D world coordinates such that the camera calibration can be bypassed. The training set for neural network consists of a variety of stereo-pair images and the corresponding 3D world coordinates. The picture elements correspondence problem is solved by using projected color-coded fringes with different orientations. Color imbalance is completely eliminated by the new color-coded method. Once the high accuracy correspondence of 2D images with 3D points is acquired, high precision 3D points cloud can be recognized by the well trained net. The obvious advantage of this approach is that high spatial resolution can be obtained by the phase-shifting technique and high accuracy 3D object point coordinates are achieved by the well trained net which is independent of the camera model works for any type of camera. Some experiments verified the performance of the method.

A light field measurement system through PSF estimation by a morphology-based method

Light field imaging technology can obtain three-dimensional(3D)information of a test surface in a single exposure.Traditional light field reconstruction algorithms not only take a long time to trace back to the original image,but also require the exact parameters of the light field system,such as the position and posture of a microlens array(MLA),which will cause errors in the reconstructed image if these parameters cannot be precisely obtained.This paper proposes a reconstruction algorithm for light field imaging based on the point spread function(PSF),which does not require prior knowledge of the system.The accurate PSF derivation process of a light field system is presented,and modeling and simulation were conducted to obtain the relationship between the spatial distribution characteristics and the PSF of the light field system.A morphology-based method is proposed to analyze the overlapping area of the subimages of light field images to identify the accurate spatial location of the MLA used in the system,which is thereafter used to accurately refocus light field imaging.A light field system is built to verify the algorithm’s effectiveness.Experimental results show that the measurement accuracy is increased over 41.0%compared with the traditional method by measuring a step standard.The accuracy of parameters is also improved through a microstructure measurement with a peak-to-valley value of 25.4%and root mean square value of 23.5%improvement.This further validates that the algorithm can effectively improve the refocusing efficiency and the accuracy of the light field imaging results with the superiority of refocusing light field imaging without prior knowledge of the system.The proposed method provides a new solution for fast and accurate 3D measurement based on a light field.

A Study of Precision Factors of Large-scale Object Surface Profile Laser Scanning Measurement

In this paper, we presented a method of using the l as er scanning triangulation for the non-contact 3D surface profile measurement of large-scale object. The characteristic of large-scale object non-contact mea surement is analyzed and the measuring method is proposed. Main factors influenc ing measurement precision such as image distortion and accurate designation of s peckle center are analyzed and methods of solving these problems are proposed. W e designed a combined filter by which the pulse noise and the Gaussian noise of speckle image can be eliminated efficiently. Using the characteristic of intensi ty distribution of laser speckle image we proposed a new approximating method th at could locate the center of laser speckle image at sub-pixel. The auxiliary v ariables are set to linearize the relationship between the image displacement an d the distance, the accurate values of laser triangulation system parameters cou ld be calibrated accurately and the measuring precision is increased remarkabl y. Using the above techniques we designed a measuring system based on laser sc anning triangulation. The results of the experiment show that these methods can raise the measuring precision of large-scale 3D surface profile effectively.

Fringe Projection Measurement System in Reverse Engineering

Acquisition of physical data with high precision is a key step in reverse engineering (RE). It is an important stimulative for the progress of reverse engineering with which various digitizing devices are invent ed, developed and made applicable. This paper introduces a three dimensional opt ical measurement method based on digital fringe projection technique in RE to im prove the technique through its application. A practical example is presented an d the result demonstrates the applicability and feasibility of the measurement s ystem as well as the reliability and validity of relevant methods and algorithms .

Robot Vision System for Coordinate Measurement of Feature Points on Large Scale Automobile Part

In this paper,we present a robot vision based system for coordinate measurement of feature points on large scale automobile parts.Our system consists of an industrial 6-DOF robot mounted with a CCD camera and a PC.The system controls the robot into the area of feature points.The images of measuring feature points are acquired by the camera mounted on the robot.3D positions of the feature points are obtained from a model based pose estimation that applies to the images.The measured positions of all feature points are then transformed to the reference coordinate of feature points whose positions are obtained from the coordinate measuring machine（CMM）.Finally,the point-to-point distances between the measured feature points and the reference feature points are calculated and reported.The results show that the root mean square error（RMSE） of measure values obtained by our system is less than 0.5 mm.Our system is adequate for automobile assembly and can perform faster than conventional methods.

Multi-Schlieren CT Measurements of Supersonic Microjets from Circular and Square Micro Nozzles

Instantaneous three-dimensional (3D) density distributions of a shock-cell structure of perfectly and imperfectly expanded supersonic microjets escaping into an ambient space are measured. For the 3D observation of supersonic microjets, non-scanning 3D computerized tomography (CT) technique using a 20-directional quantitative schlieren optical system with flashlight source is employed for simultaneous schlieren photography. The 3D density distributions data of the microjets are obtained by 3D-CT reconstruction of the projection’s images using maximum likelihood-expectation maximization. Axisymmetric convergent-divergent (Laval) circular and square micro nozzles with operating nozzle pressure ratio 5.0, 4.5, 4.0, 3.67, and 3.5 have been studied. This study examines perfectly expanded, overexpanded, and underexpanded supersonic microjets issued from micro nozzles with fully expanded jet Mach numbers Mj ranging from 1.47 - 1.71, where the design Mach number is Md = 1.5. A complex phenomenon for free square microjets called axis switching is clearly observed with two types “upright” and “diagonal” of “cross-shaped”. The initial axis-switching is 45° within the first shock-cell range. In addition, from the symmetry and diagonal views of square microjets for the first shock-cells, two different patterns of shock waves are viewed. The shock-cell spacing and supersonic core length for all nozzle pressure ratios are investigated and reported.

基于三维测量的无人艇自动靠泊引导方法研究

Automatic berthing guidance is an important aspect of automated ship technology to obtain the ship-shore position relationship.The current mainstream measurement methods for ship-shore position relationships are based on radar,multisensor fusion,and visual detection technologies.This paper proposes an automated ship berthing guidance method based on three-dimensional(3D)target measurement and compares it with a single-target recognition method using a binocular camera.An improved deep object pose estimation(DOPE)network is used in this method to predict the pixel coordinates of the two-dimensional(2D)keypoints of the shore target in the image.The pixel coordinates are then converted into 3D coordinates through the camera imaging principle,and an algorithm for calculating the relationship between the ship and the shore is proposed.Experiments were conducted on the improved DOPE network and the actual ship guidance performance to verify the effectiveness of the method.Results show that the proposed method with a monocular camera has high stability and accuracy and can meet the requirements of automatic berthing.

Laboratory Simulation of the Formation Process of Surface Geochemical Anomalies Applied to Hydrocarbon Exploration

The formation mechanisms and processes of geochemical anomalies used as proxies in surface geochemistry exploration （SGE） have not been well understood. Previous studies cannot realize 3D measurement of microseeping hydrocarbons from reservoirs to the surface, which made it difficult to understand the features and pathways of deep hydrocarbon microseepages. Understanding the processes of hydrocarbon microseepages will contribute to the acceptance and effectiveness of surface geochemistry. Based on a simplified geological model of hydrocarbon microseepages, including hydrocarbon reservoir, direct caprock, overlying strata and Quaternary sediments, this work established a 3D experimental system to simulate the mechanisms and processes of deep hydrocarbon microseepes extending to the surface. The dispersive halos of microseeping hydrocarbons in the subsurface were adequately described by using this 3D experimental system. Results indicate that different migration patterns of hydrocarbons above the point gas source within the simulated caprock and overlying strata can be reflected by the ratio of i-butane to n-butane （i-C4/n-C4）, which follow diffusion and infiltration （buoyancy） mechanisms. This is not the case for vertical measurement lines far from the point gas source. A vertical gas flow in the form of a plume was found during hydrocarbon microseepage. For sampling methods, the high-density grid sampling is favorable for delineating prospecting targets. Hydrocarbon infiltration or buoyancy flow occurs in the zones of infiltration clusters, coupling with a diffusion mechanism at the top of the water table and forming surface geochemical anomalies. These results are significant in understanding hydrocarbon microseepage and interpreting SGE data.

3D Identification of Face and Flank in Micro-mills for Automatic Measurement of Rake Angle

In an Industry 4.0 context,to each object a"digital twin"is associated,which is a virtual counterpart of the object itself.In the case of a tool,this includes,together with its material and manufacturing information,its solid geometry.Tool geometry knowledge is fundamental to enable effective tool management,manufacturing verification,and tooling simulation.If for tool management the conventional 2D presetting is sufficient,tooling simulation and tool manufacturing verification require a complete 3D characterization.This is particularly true in the case of the microtools:the process of micro-chip formation is still a research subject.Although the 3D geometry of a tool is well established in the ISO 3002 series of standard,only recently 3D measurement of tools has been made possible by new measuring systems.Still,tool geometry verification requires a lot of human intervention.This paper aims at setting the base for the automatic analysis of point meshes scanned on the whole surface of tools,and in particular microtools.The first step for doing this is the identification of the active surfaces of the tool,that is the face and the flank plus the cutting edge.The identification of these geometric features is in general possible thanks to their specific characteristics:in particular,the cutting edge is characterized by a high curvature,and it separates the face from the flank.This paper considers cylindrical micro end-mills as a first example of an approach that can be extended to in principle any kind of tool.The cylindrical helix characterizing the cutting edge is the key geometry to be considered in the development of the specific method.Once the tool features(face,flank,and cutting edge)have been separated,of the tool angles,for instance,can be estimated.As first angle to study,the rake angle has been selected.The approach will be validated on simulated data and on real scans of micro-tools.

High-speed three-dimensional shape measurement with inner shifting-phase fringe projection profilometry

Fringe projection profilometry(FPP)has been extensively studied in the field of three-dimensional(3D)measurement.Although FPP always uses high-frequency fringes to ensure high measurement accuracy,too many patterns are projected to unwrap the phase,which affects the speed of 3D reconstruction.We propose a high-speed 3D shape measurement method using only three high-frequency inner shifting-phase patterns(70 periods),which satisfies both high precision and high measuring speed requirements.Besides,our proposed method obtains the wrapped phase and the fringe order simultaneously without any other information and constraints.The proposed method has successfully reconstructed moving objects with high speed at the camera's full frame rate(1700 frames per second).

More Detailed Disturbance Measurement and Active Disturbance Rejection Altitude Control for a Flapping Wing Robot Under Internal and External Disturbances

With the goal of designing a biologically inspired robot that can hold a stable hover under internal and external disturbances.We designed a tailless Flapping-wing Micro Aerial Vehicle(FMAV)with onboard 3D velocity perception.In this way,the wind disturbance caused by the relative motion of the FMAV can be quantified in real time based on the established altitudinal dynamics model.For the rest of the total disturbance,an active disturbance rejection controller is proposed to estimate and suppress those disturbances.In comparison with the traditional PID controller,this proposed approach has been validated.The results show that,in the hovering flight with the internal unmodeled dynamics,the root-mean-square of height controlled is only 2.53 cm.Even with the different weights of loads mounting on the FMAV,the ascending trajectory of flights remains impressively consistent.In the forward flight with the external disturbance,the root-mean-square error of height controlled is 2.78 cm.When the FMAV flies over a ladder introducing an abrupt external disturbance,the maximum overshoot is only half of that controlled by the PID controller.To our best knowledge,this is the first demonstration of FMAVs with the capability of sensing motion-generated wind disturbance onboard and handling the internal and external disturbances in hover flight.

Dual-frequency fringe for improving measurement accuracy of three-dimensional shape measurement

A new phase unwrapping method based on dual-frequency fringe is proposed to improve both high accuracy and large measurement range of three-dimensional shape measurement by synthesizing the projected dual-frequency fringes obtaining higher and lower frequencies.The lower-frequency one is their phase difference,which can help unwrap the wrapped phase of the higher-frequency one from their phase sum.In addition,the relationship between the measuring accuracy and the frequencies of the projected fringes is studied to guide the frequency selection in actual measurement.It is found that the closer the two frequencies are,the higher the measurement accuracy will be.The computer simulation and experiment results show the viability of this method.

Predicting Infiltrative Hepatocellular Carcinoma Patient Outcome Post-TACE:MR Bias Field Correction Effect on 3D-quantitative Image Analysis

Background and Aims:To investigate the impact of MR bias field correction on response determination and survival prediction using volumetric tumor enhancement analysis in patients with infiltrative hepatocellular carcinoma,after transcatheter arterial chemoembolization(TACE).Methods:This study included 101 patients treated with conventional or drug-eluting beads TACE between the years of 2001 and 2013.Semi-automated 3D quantification software was used to segment and calculate the enhancing tumor volume(ETV)of the liver with and without bias-field correction on multi-phasic contrast-enhanced MRI before and 1-month after initial TACE.ETV(expressed as cm3)at baseline imaging and the relative change in ETV(as%change,ETV%)before and after TACE were used to predict response and survival,respectively.Statistical survival analyses included Kaplan-Meier curve generation and Cox proportional hazards modeling.Q statistics were calculated and used to identify the best cut-off value for ETV to separate responders and non-responders(ETV cm3).The difference in survival was evaluated between responders and non-responders using Kaplan-Meier and Cox models.Results:MR bias field correction correlated with improved response calculation from baseline MR as well as survival after TACE;using a 415 cm3 cut-off for ETV at baseline(hazard ratio:2.00,95%confidence interval:1.23-3.26,p=0.01)resulted in significantly improved response prediction(median survival in patients with baseline ETV<415 cm3:19.66 months vs.≥415 cm3:9.21 months,p<0.001,log-rank test).A≥41%relative decrease in ETV(hazard ratio:0.58,95%confidence interval:0.37-0.93,p=0.02)was significant in predicting survival(ETV≥41%:19.20 months vs.ETV<41%:8.71 months,p=0.008,log-rank test).Without MR bias field correction,response from baseline ETV could be predicted but survival after TACE could not.Conclusions:MR bias field correction improves both response assessment and accuracy of survival prediction using whole liver tumor enhancement analysis from baseline MR after initial TACE in patients with infiltrative hepatocellular carcinoma.

Error compensation for three-dimensional profile measurement system

Three-dimensional （3D） profile measurement is an indispensable process for assisting the manufacture of various optic, especially aspheric surfaces. This work presents the measurement error calibration of a 3D profile measurement system, namely PMI700. Measurement errors induced by measuring tool radius, alignment error and the temperature variation were analyzed through geometry analysis and simulation. A quantitative method for the compensation of tool radius and an alignment error compensation model based on the least square method were proposed to reduce the measurement error. To verify the feasibility of PMI700, a plane and a non-uniform hyperboloidal mirror were measured by PMI700 and interferometer, respectively. The data provided by two systems were high coincident. The direct subtractions of results from two systems indicate RMS deviations for both segments were less than 0.22.