Three-dimensional Measurement Method Research Articles

An improved DFD method for three-dimensional displacement measurement of vision-based tactile sensor

Currently, traditional tactile sensors based on the principles of capacitance or piezoelectricity have complex structures and difficulty in obtaining tactile information. A vision-based tactile sensor is introduced which can realize visual measurement of three-dimensional displacement in this paper. The vision-based tactile sensor is mainly composed of an elastomer embedded with marker point array, a transparent acrylic plate, 8 LED lights and a micro monocular camera. The elastomer deforms when the tactile sensor contacts an object, and the micro monocular camera is used to capture the elastomer deformation and transmit it to the computer in the form of image, and then the three-dimensional displacement information is obtained by processing the image. In order to more accurately recover the missing dimensional information in the three-dimensional displacement detection of monocular camera, an improved DFD (Depth from Defocus) method based on finite element theory is proposed in this paper. It is verified by experiments that the improved DFD method proposed in this paper can measure the three-dimensional displacement information more accurately compared with the DFD method. In addition, an experiment is conducted to prove the robustness of the improved DFD method on the robotic gripper. The experimental results demonstrate that the three-dimensional displacement measurement method proposed in this paper can provide technical support for the design and development of vision-based tactile sensors.

Measurement of sound scattering from a finite flat plate using a three-dimensional spatial method

The sound scattering from a finite flat plate is crucial in the scatter analysis in the water. Due to the reverberations and difficulty of determining the attitude of the finite flat plate in the water, the reflection or absorption coefficient is often used for the evaluation of the scattering properties, indirectly. A three-dimensional spatial method is proposed for directly measuring the sound scattering of a finite flat plate. The ultrasonic ranging method is utilized to determine the attitude of a finite flat plate in real-time. The complex cepstrum method is modified to extract the sound scattering from the reverberations. Using a three-dimensional spatial measurement method, a measurement system is established for measuring sound scattering from a finite stainless-steel flat plate, with a length of 1.6 m, a width of 1.2 m, and a thickness of 5 mm. The measurement results are consistent with the calculated results by a finite-element model.

Real-time motion-induced error reduction for phase-shifting profilometry with projection points tracking method

Fringe projection profilometry is a significant method for three-dimensional measurement due to its non-contact and high accuracy. However, the motion-induced error will lead to the loss of measurement accuracy in dynamic scenes due to the disruption of the phase measurement process. In this paper, we introduce a novel motion error model that considers object motion causes the misalignment of the projection points on the camera, and propose the projection points tracking method to reduce the motion-induced error. First, the speckle pattern is added to projection sequences, after which the projection point displacements are determined using the digital image correlation (DIC) method between the adjacent speckle patterns. Finally, the fringe patterns are corrected using the image remapping method to calculate the 3D shape. Quantitative analysis and dynamic measurement experiments verify the feasibility of the proposed method. Different from 3D-DIC, we use one camera-projector system to realize high-accuracy measurement in dynamic scenes.

Ultrasonic measurement method for three-dimensional assembly stress of aero-engine rotors

The precise measurement of three-dimensional stress in the rotor is a key means to ensure the assembly accuracy and operational safety of aero-engines. The unclear coupling influence mechanism of different directions of stress on ultrasonic propagation makes it challenging to establish a three-dimensional stress measurement model. This paper proposes a three-dimensional assembly stress measurement method for aero-engine rotors based on ultrasonic propagation time difference decoupling. The three-dimensional assembly stress is converted into the stress component parallel and perpendicular to the ultrasonic wave propagation direction in this method. The acoustoelastic equation including three-dimensional stress parameters is established based on the function model of different direction stress and ultrasonic wave propagation velocity. An innovative three-transducer stress measurement scheme is designed, which integrates ultrasonic wave transmitting and receiving transducers and time difference feedback transducers. The acoustoelastic equations in three propagation directions are constructed by rotating the transducer group to change the propagation direction of ultrasonic waves. Finally, the acoustoelastic equations are solved simultaneously to decouple the ultrasonic propagation time difference, thus achieving a three-dimensional assembly stress measurement of the aero-engine rotor. The experimental results show that the maximum deviation between the measured values and the simulation results in the x ,y, and z directions is 15.885 MPa, 14.113 MPa, and 17.093 MPa, respectively. This study provides effective theoretical and technical support for precisely measuring three-dimensional assembly stress in high-end equipment represented by aero-engines.

Three-dimensional surface temperature measurement using lifetime-based phosphor thermometry

Abstract In this study, we propose a three-dimensional (3D) surface temperature measurement method based on the principle of stereoscopic 3D reconstruction and the dependence of phosphorescence lifetime on temperature. A 385-nm UV(Ultraviolet) light was used as the excitation light, and two high-speed cameras were used as the detectors. The phosphor MFG (Mg4FGeO6: Mn4+) was mixed with the binder HPC and sprayed onto the tested 3D surface. The natural texture generated by the surface roughness of the phosphor coating was used as a feature for cross-correlation calculations. The digital image correlation (DIC) algorithm was used to match these feature positions in the phosphorescent images from the two cameras. The effects of the excitation angle and detecting angle were analyzed. The results indicate that the temperature measurement based on phosphorescent lifetime was not affected by the excitation and detecting angle. The method was validated on a turbine blade as an example of a 3D surface to demonstrate the capability. A comparison of the measurement results with the thermocouples proves that the current method can successfully measure the temperature on 3D surfaces with a maximum difference of 1.63°C. The spatial accuracy of the method was obtained by comparing with the measurement results of a 3D scanner, which shows that the maximum absolute error of the 3D reconstruction was 0.350 mm. The current study proposes a promising 3D surface temperature measurement method, which is expected to be widely used in gas turbine blades, Internal Combustion (IC) engine cylinders, complex curved heat exchangers, and other fields due to its non-contact measurement, low susceptibility to infrared radiation interference, high measurement accuracy, and ability to withstand harsh environments.

A Single-Camera-Based Three-Dimensional Velocity Field Measurement Method for Granular Media in Mass Finishing with Deep Learning.

Surface treatment processes such as mass finishing play a crucial role in enhancing the quality of machined parts across industries. However, accurate measurement of the velocity field of granular media in mass finishing presents significant challenges. Existing measurement methods suffer from issues such as complex and expensive equipment, limited to single-point measurements, interference with the flow field, and lack of universality in different scenarios. This study addresses these issues by proposing a single-camera-based method with deep learning to measure the three-dimensional velocity field of granular flow. We constructed a complete measurement system and analyzed the accuracy and performance of the proposed method by comparing the measurement results with those of the traditional DIC algorithm. The results show that the proposed method is very accurate in measuring spatial displacement, with an average error of less than 0.07 mm and a calculation speed that is 1291.67% of the traditional DIC algorithm under the same conditions. Additionally, experiments in a bowl-type vibratory finishing machine demonstrate the feasibility of the proposed method in capturing the three-dimensional flow of granular media. This research not only proposed a novel method for three-dimensional reconstruction and velocity field measurement using a single-color camera, but also demonstrated a way to combine deep learning with traditional optical techniques. It is of great significance to introduce deep learning to improve traditional optical techniques and apply them to practical engineering measurements.

A novel focus measure algorithm for three-dimensional microscopic vision measurement based on focus stacking

The three-dimensional (3D) microscopic vision measurement methods based on focus stacking are widely used because of their outstanding advantages such as noncontact, high accuracy, high flexibility, and low cost. On-site focus stacking 3D microscopic measurement is susceptible to environmental disturbances, surface dirt, illumination occlusion, and the shape of the object itself. This leads to the difficulty of obtaining the focus position accurately, stably, and quickly with the existing focus measure function. To improve the ability to extract the focus signals from the image, high-pass mask operators and band-pass mask operators are designed. A new high-pass and band-pass energy weighting focus measure function with rotation invariance is proposed. A focus stacking microscopic measurement system is constructed to validate the proposed focus measure function. Six classical and latest focus measure functions are selected for the quantitative performance comparison experiments. The experimental results show that the proposed algorithm has the best performance in accuracy, sensitivity, unimodality, and monotonic interval range. This measure function has a high operational efficiency, nearly three times the computational efficiency of the frequency domain measure function. The measure function also drastically reduces the evaluation curve fluctuation, peak collapse, and other anomalies, and shows good robustness.

A fast three-dimensional measurement method based on color fringe projection and background intensity calibration

A fast three-dimensional measurement method based on color fringe projection and background intensity calibration

A dataset describing chip parameters for rock breaking by chisel pick under deep-sea hydrostatic pressure

Chip is a visual representation of rock breaking by cutter, and their related parameters are crucial for revealing the rock breaking mechanism in deep-sea mining. Based on sieving and three-dimensional size measurement methods widely used in mining engineering, this paper reports a dataset of chip parameters for rock breaking by chisel pick under deep-sea hydrostatic pressure. Specifically, we first designed an experimental setup that can accurately simulate deep-sea hydrostatic pressure, conducted rock breaking experiments and carefully collected chips. Subsequently, those chips were sieved, high-resolution images were collected, and the coarseness index (CI), chip size uniformity (n), absolute chip size (de), and fractal dimension (D) were measured. Finally, three-dimensional size (long, intermediate and short) was measured for 3064 chips with particle sizes greater than 4.75 mm. This dataset will be used by researchers to validate numerical simulations or optimize equipment structures related to deep-sea mining, including deep-sea rock mechanics, mining cutter and conveyor pipes.

Fast high-precision 3D shape measurement using linear phase encoding with geometry constraints

A three-dimensional (3D) profile measurement method based on geometric constraints combined with linear phase encoding (GCPE) is proposed. This method encodes the wrapped phase and the linear signal in the same phase domain, achieves the elimination of the phase ambiguity within the local fringe period, and obtains an unambiguous absolute phase within the entire period through geometric constraints. Compared with the traditional phase encoding method, this method solves the problem of period sequence errors caused by a large number of codewords by encoding linear signals in the phase domain and using a period order correction method to deal with the period jump phenomenon caused by noise. At the same time, the measurement range of the fringe projection system under geometric constraints is significantly improved. Experimentally, 3D profiles of standard planes, complex statues, and separated objects were measured by the use of the GCPE. The results show that the GCPE has the advantage of fast speed and high accuracy in measuring the 3D profile of objects.

Highly accurate three-dimensional measurement of large structures using multiple stereo vision with improved two-step calibration algorithm

A multiple stereo-based three-dimensional (3D) measurement method of large-scale structures is presented, which replaces time-consuming and laborious 3D measurement procedure of laser-based conventional equipment. To have 3D reconstruction accuracy with millimeter-precision, two-step calibration algorithms are improved. Specifically, we use 2D epipolar constraint, using fundamental matrix determined by matched points, to new combination of objective function for intrinsic parameter calibration. We additionally propose an onsite structure parameter calibration algorithm using different epipolar constraint of measurement points in images of large ship block as well as reprojection error of checkerboard, to bypass the limitation of the coverage of checkerboard in large-scale measurement. The actual 3D measurement of the three ship blocks is conducted, and the 3D reconstruction accuracy is validated by comparing the 3D coordinates measured by total station. The experimental results showed that the mean 3D reconstruction error ranged from 6 to 14 mm.

A three-dimensional algorithm for precise measurement of human auricle parameters

Measurement of auricle parameters for planning and post-operative evaluation presents substantial challenges due to the complex 3D structure of the human auricle. Traditional measurement methods rely on manual techniques, resulting in limited precision. This study introduces a novel automated surface-based three-dimensional measurement method for quantifying human auricle parameters. The method was applied to virtual auricles reconstructed from Computed Tomography (CT) scans of a cadaver head and subsequent measurement of important clinically relevant aesthetical auricular parameters (length, width, protrusion, position, auriculocephalic angle, and inclination angle). Reference measurements were done manually (using a caliper and using a 3D landmarking method) and measurement precision was compared to the automated method. The CT scans were performed using both a contemporary high-end and a low-end CT scanner. Scans were conducted at a standard scanning dose, and at half the dose. The automatic method demonstrated significantly higher precision in measuring auricle parameters compared to manual methods. Compared to traditional manual measurements, precision improved for auricle length (9×), width (5×), protrusion (5×), Auriculocephalic Angle (5–54×) and posteroanterior position (23×). Concerning parameters without comparison with a manual method, the precision level of supero-inferior position was 0.489 mm; and the precisions of the inclination angle measurements were 1.365 mm and 0.237 mm for the two automated methods investigated. Improved precision of measuring auricle parameters was associated with using the high-end scanner. A higher dose was only associated with a higher precision for the left auricle length. The findings of this study emphasize the advantage of automated surface-based auricle measurements, showcasing improved precision compared to traditional methods. This novel algorithm has the potential to enhance auricle reconstruction and other applications in plastic surgery, offering a promising avenue for future research and clinical application.

Three-dimensional micro-force measurement method based on broadband optical coherence

In response to the high-precision and multi-dimensional force measurement requirements in the fields of biology and medicine, this paper proposes a novel three-dimensional microforce measurement method based on the broadband optical coherence. A novel, compact, and low-coupling elastic element was designed, with a maximum outer diameter of 26 mm and a capacity of 50 g in the X-, Y-, and Z-directions, respectively. The functional relationship between the displacements of the three detecting points on the elastic element and the applied external force was derived based on the elastic mechanics theory. And it was also verified by the finite element method. A self-built optics system was set up to sense the displacements of the three points on the elastic element. The experiments results showed that the resolution in the X-, Y-, and Z-directions was 0.10 mN, 0.11 mN and 0.13 mN, respectively. In the measuring range of (10–50) g, the maximum coupling rate was 4.55 %, and the maximum linear error was 4.70 %. The maximum repeatability error was only 0.615 %. The method and sensor were verified with good characteristics of high resolution, low coupling rate, high linearity and high accuracy, comparing to other reported researches. The multi-dimensional force measuring method could be used in the fields of biology and medicine.

Three-dimensional measurement method based on reusing equally spaced binary stripes

To eliminate the effect of nonlinear errors on measurement results, this paper presents a new method, to our knowledge, to overcome the nonlinear response of commercial projectors and cameras by using binary stripes for coding. The method shifts the generated equally spaced binary stripes by a fixed number of pixel points to obtain different stripe maps, followed by sequential projection of these binary stripes with a digital projector. The acquired binary stripes are reused in the 3D reconstruction combined with the phase-shift method and can be reduced to sinusoidal stripes with different phase shifts by a specific superposition method. In this paper, this method is combined with the traditional four-step phase-shift method for experiments. The results show that the accuracy of the wrapped phase obtained by the method proposed in this paper is 13.88% higher than that obtained by the traditional 16-step phase-shift method. Similarly, the accuracy of the standard ball measurement is increased by 21.05%. Additionally, the point cloud on the surface of the complex object obtained by the proposed method is smoother and more delicate than that obtained by the traditional 16-step phase-shift method.

Object phase-valid region segmentation method for FPP-based three-dimensional measurement

In most existing studies based on fringe projector profilometry (FPP), the whole scenario is reconstructed, or the ideal experimental settings are established to segment the object easily. However, in real industrial scenarios, automated object detection and segmentation are essential to perform object-level measurement. To address the problem, a dual-wavelet feature interaction network (DWFI-Net) is developed in this paper to perform object phase-valid region segmentation, where both the background and shadow are removed. In our work, the modulation and wrapped phase maps are considered as inputs innovatively. The modulation maps provide abundant structures and textures, while the wrapped phase maps complement and enhance shadows and edges. An adaptive wavelet feature interaction (AWFI) module is presented to learn and fuse the features, where discrete wavelet transformation (DWT) is applied to decompose the features. An edge-aware discrete cosine transformation (EDCT) module is developed as a decoder, where the discrete cosine transformation (DCT) is applied to interpret the fused features. Qualitative and quantitative experiments are performed to verify the superiority of our DWFI-Net and its effectiveness on object-level three-dimensional measurement based on FPP.

Calibration for endoscopic 3D shape measurement with cone beam projection

We demonstrate a calibration method for endoscopic three-dimensional shape measurement with cone beam projection. In this method, changes in the shape of the optical sectioning profiles are quantified and fitted while scanning a calibration board in the depth direction, using a cubic function. In accuracy tests using a flat plate and a ring reference gauge, the proposed method obtains an accuracy of 0.02 mm in the depth dimension and 0.09 mm in the radial dimension. These results represent 88% and 55% improvements compared to previous analysis. For medical applications, an ear examination simulator was employed, and our measurement results were compared to ground truth data obtained by microfocus X-ray computed tomography. The surface deviation of our method relative to the ground truth data was ±0.36mm during manual operation. A comparison of the measurement results before and after calibration revealed an improvement in the peak agreement with the ground truth data, with the deviation shifting from 0.2 mm to −0.05mm. Our strategy achieves a digital transformation of 3D endoscopy, which would benefit a number of medical fields.

Three-dimensional measurement method of binary particle collisions under dry and wet conditions

The description, calculation and design of solids processes, such as fluidization, pneumatic conveying or mixing, require knowledge of collision dynamics between particles and apparatus walls or interparticle collisions without, but often also with the presence of an additional liquid. For the study of such dry and wet interparticle collisions, an experimental setup is presented that allows the performance of dry or wet free binary collisions of spherical particles down to a minimum diameter of 1 mm. The recording of the particle motions in all three spatial directions is provided by two synchronized highspeed cameras. Methods and algorithms are presented for analyzing the translational and rotational motion in three-dimensional space, as well as for measuring the amount of liquid on the particles in the case of wet collisions. Motion data from dry collisions between equal sized and unequal sized spherical particles are compared with a three-parameter collision model. In addition, a first series of measurements of wetted collisions is used to compare the collision dynamics with dry collisions.

Dynamic three-dimensional deformation measurement by polarization-multiplexing of full complex amplitude.

This paper provides an extensive discussion of a complex amplitude-based dynamic three-dimensional deformation measurement method, in which the phase and amplitude of the speckle field are used for out-of-plane and in-plane deformation calculation respectively. By determining the optimal polarization states of the speckle field and reference field from the comprehensive analysis of measurement mathematical model in the principle of polarization multiplexing, the 3-step phase-shifting interferograms and one speckle gram can be directly recorded by a polarization camera in a single shot. The out-of-plane deformation would be recovered from the subtraction of speckle phases that are demodulated by a special least square algorithm; speckle gram with improved quality is offered for correlation computation to obtain in-plane deformation. The advancement and significance of the optimized strategy are intuitively demonstrated by comparing the measurement accuracy under different combinations of polarization states. Finally, the dynamic thermal deformation experiment reveals the potential in practical real-time applications.

Binocular Visual Measurement Method Based on Feature Matching.

To address the issues of low measurement accuracy and unstable results when using binocular cameras to detect objects with sparse surface textures, weak surface textures, occluded surfaces, low-contrast surfaces, and surfaces with intense lighting variations, a three-dimensional measurement method based on an improved feature matching algorithm is proposed. Initially, features are extracted from the left and right images obtained by the binocular camera. The extracted feature points serve as seed points, and a one-dimensional search space is established accurately based on the disparity continuity and epipolar constraints. The optimal search range and seed point quantity are obtained using the particle swarm optimization algorithm. The zero-mean normalized cross-correlation coefficient is employed as a similarity measure function for region growing. Subsequently, the left and right images are matched based on the grayscale information of the feature regions, and seed point matching is performed within each matching region. Finally, the obtained matching pairs are used to calculate the three-dimensional information of the target object using the triangulation formula. The proposed algorithm significantly enhances matching accuracy while reducing algorithm complexity. Experimental results on the Middlebury dataset show an average relative error of 0.75% and an average measurement time of 0.82 s. The error matching rate of the proposed image matching algorithm is 2.02%, and the PSNR is 34 dB. The algorithm improves the measurement accuracy for objects with sparse or weak textures, demonstrating robustness against brightness variations and noise interference.

Varus/valgus stability in imageless robotic-assisted total knee arthroplasty applying three-dimensional assessment of varus/valgus stress X-rays.

The postoperative varus/valgus stability assessment in stress X-rays has been established as an evaluation index. However, it is performed by the two-dimensional (2D) method rather than the three-dimensional (3D) method. This study aimed to identify the precision and reproducibility of measuring varus/valgus stress X-rays three-dimensionally and to examine varus/valgus stability under anesthesia in imageless robotic assisted total knee arthroplasty (rTKA). This prospective study analyzed 52 consecutive rTKAs (five males, 67 ± 5.3 years; 47 females, 74 ± 5.9 years). Postoperative varus/valgus stress X-rays in knee extension under anesthesia at manual maximum stress were three-dimensionally assessed by 2D-3D image matching technique using the 3D bone and component models. Varus/valgus angle between components (VV angle) in no stress, valgus stress, varus stress, medial joint opening (MJO), and lateral joint opening (LJO) were evaluated, clarifying this method's precision and reproducibility and valgus/varus stability. All parameters' precision and reproducibility had <1° mean differences and high intra- and inter-class correlation coefficients. Bland-Altman plots showed no fixed and proportional bias. Non-stress VV angle, valgus VV angle, varus VV angle, MJO, and LJO were 3.6 ± 1.2°, 1.0 ± 1.4°, 7.1 ± 1.9°, 1.5 ± 1.0mm, and 2.8 ± 2.7mm, respectively. This prospective study demonstrated that (1) the three-dimensional measurement method provided sufficient precision and reproducibility, and (2) the rTKAs could achieve good postoperative varus/valgus stability with a small standard deviation.