3D measurement system based on divergent multi-line structured light projection, its accuracy analysis

Line-structured light 3D measurement is often used for 3D contour reconstruction of objects in complex industrial environments, where light plane calibration is a key step. In this paper, we propose a calibration method for a line-structured optical system based on a hinge-connected double-checkerboards stereo target. First, the target is moved randomly in multiple positions at any angle within the camera measurement space. Then, by acquiring any one image of the target with line-structured light, the 3D coordinates of the light stripes feature points are solved with the help of the external parameter matrix of the target plane and the camera coordinate system. Finally, the coordinate point cloud is denoised and used to quadratically fit the light plane. Compared with the traditional line-structured measurement system, the proposed method can acquire two calibration images at once; thus, only one image of line-structured light is needed to complete the light plane calibration. There is no strict requirement for the target pinch angle and placement, which improve system calibration speed with high accuracy. The experimental results show that the maximum RMS error of this method is 0.075mm, and the operation is simpler and more effective to meet the technical requirements of industrial 3D measurement.

A composite-structured-light 3D measurement method based on fringe parameter calibration

A calibration method for line-structured light system by using sinusoidal fringes and homography matrix

Background This study aimed to investigate factors, such as differences in femoral shape, that could affect the femoral valgus correction angle (VCA) for the intramedullary alignment rod (IM rod) by using a three-dimensional (3D) measurement system in patients with varus knee osteoarthritis undergoing total knee arthroplasty (TKA). Methods A total of 305 knees in 233 Japanese patients with varus knee osteoarthritis who underwent primary TKA by using Jig Engaged 3D Pre-Operative Planning Software for the TKA operation support system was examined. We retrospectively analysed factors, such as the shape of the proximal, middle, and distal femur in the coronal plane, all of which could affect the VCA for the IM rod, by multiple linear regression analyses. Results The VCA for the IM rod was 5.9° ± 1.6° (range: 1.7° to 10.7°), and the femoral lateral bowing angle (FBA) was 3.5° ± 3.2°. Major factors independently associated with the VCA for the IM rod were the FBA (β: 0.75), femoral offset (β: 0.38), and the medial angle between the mechanical femoral axis and the line that connects the distal margins of the medial and lateral femoral condyles (β: −0.16). The model was created by stepwise multiple linear regression (F = 266.6, p < 0.001, and estimated effect size = 4.4) explained 85% of the variance in the VCA for the IM rod (R2 = 0.85). Conclusions The VCA for the IM rod was most strongly associated with femoral lateral bowing in patients with varus knee osteoarthritis undergoing TKA. Our findings suggest that preoperatively measuring the VCA for the IM rod in patients with femoral lateral bowing by using a 3D measurement system could be useful for accurate coronal alignment of the femoral component in TKA.

A three-dimensional (3D) measurement system with spectroscopic function was demonstrated using a practical supercontinuum light source and an all-fiber interferometer. Spectral information was obtained by Fourier transformation of the observed interference signal. We obtained the absorbances of various plastics. In addition, the system was capable of discerning different surface asperities that were smaller than the spatial resolution of the system by observing the spectral modulation caused by spectral interference that occurred when there was an asperity in the irradiated beam spot. The frequency of the spectral modulation depended on the height of the asperity. In this paper, the spectral modulation was analyzed by numerical calculations, and images based on the spectral modulation differences were obtained experimentally. The longitudinal and transverse resolutions were 3.0 and 125 µm, respectively. Based on the spectral modulation, we demonstrated that our 3D measurement system could obtain images of asperities of diameters 3, 6, 15, and 90 µm, which were smaller than the spatial resolution. A clear 3D image of a metallic cylinder with a small blemish was also obtained using this system.

Multi-line laser projection 3D measurement simulation system technology

Light plane calibration and accuracy analysis for multi-line structured light vision measurement system

A PC-based stereoscopic imaging and measurement system (SIMS) was developed for undersea applications. The SIMS is capable of real-time image capture, recording and stereoscopic display as well as on-fine/on-demand 3-D measurement. The SIMS consists of a pair of underwater cameras, a controller, a pair of digital video recorders (DVRs), a PC to house the CPU, DVRs, hard drives, and other peripherals, and an autostereoscopic display. The cameras can be either mounted on a remotely operated vehicle (ROV) or carried by a diver to capture underwater scenes. Stereoscopic images are viewed on the glasses-free autostereoscopic display. Software modules were developed and/or adopted from published computer codes to operate the SIMS. Operations include those described above, camera calibration, and on-line/on-demand 3D measurement of features on the target objects. A virtual 3D camera calibration scheme was extended from a camera calibration method which captures the images of a coplanar checkerboard at several perspectives. The performance of the SIMS prototype for 3D measurement was evaluated by comparing the measured and actual distances between the checker corners on the checkerboard and between markers painted on a fish silhouette at several angles of orientation.

Association of Outflow Cannula Angulation with Adverse Neurological Events in Patients with CF-LVAD

In the process of intelligent manufacturing, all kinds of complex workpieces in aerospace, automobile and other fields need to be measured and identified with high precision, so that industrial robots can sort or assemble the workpieces. The structure of the workpieces is complex, the surface texture is weak, and they are scattered and stacked on the automatic production line, so there are some problems such as low accuracy of three-dimensional (3D) measurement and positioning and low efficiency. To solve these problems, a high precision positioning method based on robot-driven 3D measurement is proposed. Firstly, the 3D point cloud data of the complex workpieces is obtained from the structured light 3D measurement device, and then the point cloud data is processed by the sampling consistent initial registration algorithm (SAC-IA) and the iterative nearest point algorithm (ICP). Through the rough estimation and accurate solution of the position and attitude of the workpiece, the 3D attitude of the workpieces in the coordinate system of the structured-light 3D measurement device is obtained. Finally, the spatial pose solution algorithm is used to calculate the 3D attitude of the workpieces in the robot coordinate system and guide the robot to grasp automatically. The experiments show that the grasping position error is 0.34mm, and the grasping angle error is 0.36°. It can accurately measure and identify the point cloud target, calculate the 3D attitude of the complex workpieces, and accurately guide the robot to grab the workpiece automatically, which can be popularized and applied in the industry.

Measurement is an important means for humans to understand and transform the world, and it is the technological foundation for breaking through the forefront of science and solving major problems in economic and social development. The three-dimensional measurement system serves primary national needs, leads national economic development, and ensures national defense security. With the arrival of a new industrial revolution, major industrial countries worldwide have begun to accelerate the strategic deployment of intelligent manufacturing. As an essential component of the construction of smart factories and lighthouse factories, the 3D measurement system will play a vital role in deepening the implementation of the manufacturing power strategy and promoting the high-end, intelligent, and green manufacturing process. In recent years, optical 3D measurement technology represented by surface structured light has developed rapidly and has been widely applied in multiple material processing fields such as forging, casting, and sheet metal. To analyze the manufacturing accuracy of complex parts using surface structured light 3D measurement technology, it is necessary to first scan and reconstruct the overall 3D surface of the part. The reconstructed 3D point cloud data of the part surface should be roughly and precisely matched with the design model. Finally, based on this, data comparison and accuracy analysis should be carried out according to the actual detection requirements of different types of parts. In this process, the accuracy of 3D reconstruction of complex parts and the alignment accuracy between the reconstruction results and the design model directly determine the reliability and accuracy of the final part manufacturing and machining accuracy analysis. This article uses cases to illustrate the application of machine vision in 3D online measurement. The application of three-dimensional measurement technology in online quality inspection and grinding of blades can not only improve the measurement accuracy of online quality inspection of blades but also maintain the relative stability of robot grinding force and improve the grinding effect in robot grinding of aircraft engine blades. Applied to online quality inspection of train wheel hubs, three-dimensional measurement of train wheel adapters and high-speed train wheel size online inspection has been achieved.

Analysis and compensation of lateral chromatic aberration of structured light 3D measurement system

The line structure light three-dimensional reconstruction system is a kind of three-dimensional non-contact measurement system, which has the advantages of high precision, high speed, small damage to objects and strong adaptability. Camera calibration is a major factor that constrains the accuracy of 3D measurement systems. The camera calibration is based on the pinhole imaging model, and through a series of complex calculations, the camera’s internal parameters (focal length, distortion coefficient) and external parameters (rotation matrix and translation vector). The different calibration methods use different calibration targets, which can be divided into 3D calibration targets, 2D calibration targets, and one-dimensional calibration targets according to the characteristics of the calibration targets. This paper mainly discusses: calibration content and significance, calibration methods for different targets and evaluation methods for calibration of different targets. Firstly, the content and significance of calibration are expounded. Then, according to different calibration targets, the calibration algorithm is analyzed. Finally, the calibration algorithm is analyzed and summarized, and the development trends, advantages and disadvantages of different calibration methods are pointed out.

With the appearance of low-cost and high-resolution consumer-grade digital cameras, a practical three-dimensional (3D) measurement system using a consumer-grade digital camera is greatly anticipated in various fields. In these circumstances, the authors have been concentrating on developing a practical 3D measurement system that includes photogrammetric software called the Image Based Integrated Measurement (IBIM) system. The IBIM system device consists of full/half-mirrors, a consumer-grade digital camera, and a laser distance meter. The most remarkable advantage of the system is its ability to calculate exterior orientation parameters, interior orientation parameters, and pseudo ground control points (GCPs) without using scale bars or the GCPs in the object field. The system has the ability to calibrate multiple cameras of different resolutions using a camera-variant parameter set. However, there remains one issue that needs to be resolved before this system can be effectively used, namely, improvement of the system which does not depend on the IBIM system device. With this motive, a practical photogrammetry method using a consumer-grade digital cameras and a hand-held laser distance meter is proposed. To test our proposed method, the bundle of distances from the center camera position to the feature points in the object field were measured individually at archaeological sites in Greece. In order to evaluate the possibility and practicability of the proposed photogrammetry method, this paper describes and evaluates the camera calibration techniques using images from multiple cameras of different resolutions and a bundle of distances.

Assessment of process chain suitability of the optical 3D measuring system by using influencing factors for measurement uncertainty