Multi-line Structured Light Research Articles

Identifying the Laser Stripes via Ray Model for Multiline Structured Light Stereo Vision Sensors

Identifying the Laser Stripes via Ray Model for Multiline Structured Light Stereo Vision Sensors

A Multiline Structured Light Sensor-Based System for Measuring the Geometries of Train Wheelsets

A Multiline Structured Light Sensor-Based System for Measuring the Geometries of Train Wheelsets

Multi-line structured light stripes clustering based on a custom iterative window

ObjectiveThis paper proposes a multi-line structured light stripe clustering method based on a custom iterative window to address the issue of stripes confusion caused by stripe breakage and noise points during the multi-line laser stripe matching process in binocular stereo vision. MethodsFirstly, the paper segments the measured object from the carrier plane. Secondly, the extracted centerlines are clustered using the custom iterative window. Finally, the stripes are numbered one by one after clustering the left and right images using barycentric coordinates of the stripes, based on the property of sequential consistency constraint, to complete the stereo matching of the stripes with the same number. ResultsThe experimental results show that the method can effectively cluster the centerline stripes on the measured object and solve the problem of stripes mis-corresponding when stereo matching of multi-line structured light stripes.

High accuracy calibration method for multi-line structured light three-dimensional scanning measurement system based on grating diffraction.

Multi-line structured light three-dimensional (3D) scanning measurement system enables to obtain the richer 3D profile data of the object simultaneously during one frame, ensuring high accuracy while structured light is deformed for the modulation by the object. Nevertheless, current calibration methods cannot fully take advantage of its high precision. In this paper, a fast and high-accuracy 3D measurement system based on multi-line lasers with a spatially precise structure via integrating a diffraction grating was proposed. This helps achieve precise calibration results of the light planes by introducing spatial constraint relations of the diffractive light, thus improving measurement accuracy. The operating principle and the workflow of the proposed system were described in detail. The measurement accuracy of the developed prototype was verified through contrastive experiments. At a working distance of 400 mm, the results show that the root mean square error (RMSE) of the proposed system is 0.083 mm, which is improved by 37.6% compared to the traditional calibration method of light planes for the ranging system. The system utilizing a grating that facilitates the integration of the device has great application value.

Research on the angle measurement system of bending workpieces based on multi-line structured light

Research on the angle measurement system of bending workpieces based on multi-line structured light

Clustering of divergent multi-line structured light stripes based on structural constraint

Aiming at the confusion between multi-line structured light stripes in the 3D measurement system based on divergent multi-line structured light projection, an effective clustering method of multi-line structured light stripes based on structural constraint is proposed in this paper. The light stripes are numbered, and the light stripe image collected by CCD camera are divided into regions. According to the formula proposed in this paper, the region parameters are calculated, and the number of each light stripe is recognized to realize the clustering of line structured light stripe. Experimental results show that this method effectively avoided the confusion between light stripes.

Preprocessing of multi-line structured light image based on Radon transformation and gray-scale transformation

In the process of the structured light detection, it is affected by many factors such as the light source, object to it-self and environmental noise, which result in poor imaging quality. For this reason, the Radon transformation of multi angle is adopted to get the transform domain image, after obtaining the information of the oblique angle of the structured light stripes. After that the singular points unrelated to the target stripes are eliminated in the transform domain image. Then the processed transform domain image is restored and the noise is eliminated. At the same time, the above-mentioned structured light images are pre-processed by several existing means to eliminate noise. Then compared with the traditional methods, the superiority of the Radon transformation in eliminating noise interference is highlighted by using the reliability evaluation scheme to evaluate the quality of the processed images. Finally, aiming at the other shortcomings in the Radon transformed image and further improving the image quality, the restored images are handled by the gray-scale transformation enhancement to enhance the overall gray level of the image. The experimental results show that the imaging quality of the image processed by the above methods is significantly improved.

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

This paper investigates the overall fitting accuracy of the light plane can be improved by changing the relative distance between camera and laser, altering the projection direction of the light stripe and increasing the number of extracted light stripe in the multi-line structure light measurement system. Firstly, a multi-line structured light three-dimensional measurement system platform is built, and the existing calibration plate is modified according to the requirements of the experimental design. Then, laser stripes are projected onto a blank area in the checkerboard to facilitate the extraction of the centerline of the light stripe. Moreover, the three-dimensional (3D) point cloud transformed from centerline of each stripe is used to fit into a plane by a random sample consensus algorithm (RANSAC). Finally, the influence of different experiment methods on the overall fitting accuracy of the light plane is observed. Experiments illustrate that the proposed experimental methods can reduce the relative error of the overall fitting result of the multi-line structured light plane by more than two times, and the overall calibration accuracy of the light plane is improved in terms of the error of angle between the calibrated light planes.

Efficient Measurement of Key-Cap Flatness for Computer Keyboards With a Multi-Line Structured Light Imaging Approach

A computer keyboard is an important human–machine interaction device. A key-cap and a keyboard are flexibly connected, and its assembly quality, especially flatness, is crucial. In manufacturing quality control, the requirement for assembly quality of keyboards is quite strict, where the flatness measurement of key-caps is a key link. In this paper, an apparatus based on multi-line structured light imaging, and machine vision is designed for online rapid detection of key-cap flatness, is proposed. First, a novel 3D measurement scheme is presented to replace the complete 3D surface reconstruction of conventional methods. Then, an array of cameras with a perspective projection transformation matrix calibration approach is adopted to expand the scanning range of the 3D sensor for large-scale and high-resolution target imaging. In addition, a multi-step image processing is applied to accurately extract the centerline of the projected fringes on a key-cap with printed character, which indirectly helps to improve the measurement accuracy. Finally, a sparse sampling flatness estimation algorithm is proposed to improve the detection efficiency. According to experiments in real production lines, our apparatus can achieve a detection accuracy of 99.74% for various computer keyboards.

Distortion Rectifying for Dynamically Measuring Rail Profile Based on Self-Calibration of Multiline Structured Light

Dynamically measuring rail profile using the structured-light vision suffers from random vibrations on the line laser projector, which would cause distorted rail profiles. This paper presents a simple and effective distortion rectifying method to address this issue. The distorted rail profile is rectified by easily projecting it onto an auxiliary plane which is parallel to the cross section of rail. In order to establish the auxiliary plane, three profiles formed by radiating multiline structured light on rail are used to fit the rail longitudinal axis. More importantly, only one of the light planes is required to be calibrated beforehand. The others are calibrated online with the proposed self-calibration method, which is based on collinearity and parallelity constraints on the scene points of different rail profiles and requires only one image of the scene. Apart from evaluating the implementation with comprehensive experiments, we compare our method against other published works. The results exhibit its effectiveness and superiority in terms of the dynamic measurement of the rail profile.

Applying Structured Light on Cylinder Straightness Detection Using Break Line Method

Generally after a cylindrical steel bar is made from hot forming process, its contour will look like ‘U’ or ‘wavy’ topography. The preformed steel bar after steelmaking process needs to remove the outside oxide layer by lathe or peeling machine (commonly known as stripping). As a consequence, the deformation of steel bar will cause subsequent problems, such as eccentric rotating of steel bar as the lathe is running. Although it is necessary to remove the oxide layer, the deformation will increase waste materials. To prevent the problems, a straightening machine is usually used to straighten the cylindrical steel bar before the pickling process. However, most current straightening machines cannot measure cylindrical steel bar contour on-line instantly. This study proposed a test method for measure the contour of a large cylindrical steel bar based on multi-line structured light and machine vision. Break line method were performed to measure the contour of the cylindrical steel bar. The experimental result shows that the measurement error is in the range of ±0.4 mm after calibration. The study result concludes that the proposed method can be applied to straightening machine for real-time online measurement to improve straightening efficiency.

Study on Scattered Data Points Interpolation Method Based on Multi-line Structured Light

Aiming at the range image obtained through multi-line structured light, a regional interpolation method is put forward in this paper. This method divides interpolation into two parts according to the memory format of the scattered data, one is interpolation of the data on the stripes, and the other is interpolation of data between the stripes. Trend interpolation method is applied to the data on the stripes, and Gauss wavelet interpolation method is applied to the data between the stripes. Experiments prove regional interpolation method feasible and practical, and it also promotes the speed and precision.

Large 3D free surface measurement using a mobile coded light-based stereo vision system

A mobile coded light-based stereo vision system for measuring large 3D free surface is proposed. The system combines the technology of binocular stereo vision and multi-line structured light, which simplifies the process of finding correspondence. It can be freely moved around measured objects, and acquires local 3D data in various viewpoints. The methods of extracting light stripe are outlined. A novel approach, pyramid sub-grate projecting approach, is developed for encoding structured light. The approach can subdivide a high-density light grate into multiple sparse sub-grates. Each of the sub-grates can be effortlessly encoded by the time-multiplexing coding method. Given a point on left image, the correspondent point on right image is the intersection of coded light stripes with the same code and epipolar line. Then, the depth is estimated by triangulation. Moreover, a new registering 3D data based on a planar baseline target is detailed. The mathematic model of this registration method is given. An objective function about all parameters of rotation matrix and transmission vector being established, and those parameters can be found by Levenberg-Marquardt optimization Algorithm. However, the transmission vector is scaled by an unknown coefficient. Then the method of ascertaining the coefficient is also described. Compared with iterative closest point (ICP) algorithm, a popular registration method, the present registering method costs much less time, and is suitable for all kinds of objects. Some experimental results are presented to demonstrate the proposed technology. The results show that high-resolution 3D data of free surface has been acquired and 3D data have been perfectly registered.