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A robust model-based calibration method for dual laser line active triangulation range cameras, with the goal of reducing camera occlusion via data fusion, is presented. The algorithm is split into two stages: line-based estimation of the lens distortion parameters in the individual cameras, and computation of the perspective transformation from ea...
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... Motion planning of laser sensors benefits from its similarity to production technologies where path-oriented systems are widely used [12], including milling, grinding, roller burnishing [13] and spraying. In addition to concern with tool collision, with a laser sensor there are also concerns with occlusion of either the laser or the camera [11,14,15]. ...
Nowadays, computerized dimensional inspection is included in most manufacturing processes. Industrial vision systems, laser triangulation sensors (LTS) in particular, are responsible for ensuring dimensional and geometrical tolerance compliance. Computer-aided design / computer-aided engineering (CAD/CAE) plays an important role in the manufacturing process. However, in the design and engineering of LTS, there is no equivalent computer-aided tool to provide assistance to the process definition. This paper presents a simulation environment to assist with this issue. Based on the CAD files of the parts, all the parameters of an LTS sensor and its scanning strategy can be simulated in a virtual Direct3D environment. This simulation provides a re-creation of the camera acquisition, allowing collision and occlusion detection and ensures complete and effective digitalization. Furthermore, the capability of the process of tolerance compliance evaluation can be verified. Once the effectiveness of the process is proven, the simulation can be employed for continuous performance improvement and the incorporation of new parts.
... Configurations with single cameras are well-studied; multiple-camera cofigurations are less common, but are beginning to find use in industry. We assume that multiple-camera configurations are mutually calibrated: see treatments by Saint-Marc et al. [17], Vilaça et al. [18], and Mavrinac et al. [19]. ...
... with z H (H, p) = Hh sin ζ(p) tan α l + tan α r (19) where ζ(p) is the view angle to p, as given by (23). (19) is derived similarly to (17), with the additional term accounting for the effect of the oblique angle of incidence. ...
A semiautomatic model-based approach to the view planning problem for high-resolution active triangulation 3-D inspection systems is presented. First, a comprehensive, general, high-fidelity model of such systems is developed for the evaluation of configurations with respect to a model of task requirements, with a bounded scalar performance metric. The design process is analyzed, and the automated view planning problem is formulated only for the critically difficult aspects of design. A particle swarm optimization algorithm is applied to the latter portion, including probabilistic modeling of positioning error, using the performance metric as an objective function. The process leverages human strengths for the high-level design, refines low-level details mechanically, and provides an absolute measure of task-specific performance of the resulting design specification. The system model is validated, allowing for a reliable rapid design cycle entirely in simulation. Parameterization of the optimization algorithm is analyzed and explored empirically for performance.
... Odwzorowanie zatem w układzie triangulacyjnym nie jest -jak w przypadku obrazu ze zwykłej kamery -przestrzeni 3D na obraz 2D, lecz jednej płaszczyzny dwuwymiarowej, wyznaczonej światłem laserowym, na drugą, będącą powierzchnią rejestratora kamery. Pomijając zniekształcenia optyczne, opisane w rozdziale 8.1, można to przekształcenie zapisać w postaci homografii [45,[53][54][55], definiowanej równaniem (8.6). ...
... stopniowane [54,[142][143][144], piłozębne [145,146], płaskie tarcze z nadrukowanymi punktami charakterystycznymi wykorzystywane także do kalibracji dystorsji [44,45,141,144,147,148]. ...
... Dzięki niej wyznaczana jest transformacja pomiędzy współrzędnymi przetwornika, a współrzędnymi obiektu rzeczywistego. Bazuje ona na metodzie opisanej w [54,145,151]. W procesie kalibracji wykorzystywany jest wzorzec posiadający z jednej strony płaską powierzchnię, a z drugiej zarys piłokształtny (rys. 8.5), który fotografowany jest w różnych oddaleniach, zgodnie z osią skanowania. ...
In the industry, especially automotive, the most important criterion of quality is the dimensional accordance with specification. Keeping the dimensional tolerances given by the constructor is critical from the reliability and life time point of view. For this reason, an important role in quality control play the coordinate measurements. On the market there are many coordinate measuring machines intended not only to work in the laboratory, but also on the production line. Their manufacturers have developed applications for a very wide range of applications. From small, to measure the precise details, of the size in scale of centimetres until large, having workspaces that allow for the measurements of the whole body of vans. All these machines are characterised by very large accuracies, and in addition, due to the classic, tactile nature of measurement, are relatively easy to validate. For this reason, until recently such machines were the only used in the field of geometrical quality inspection. Their main disadvantage is, however, very little speed and often limited possibility of full automation. Therefore, 100% control by means of measuring machines is impossible in large scale production. For this reason, the role of optical devices grows. Data from German industry, the most representative in terms of development trends, show that about 30% of production enterprises are going to change the current solutions to 3D non-contact optical systems and the trend is rising.
Optical measuring devices, particularly those that are based on the image analysis, allow the acquisition of more points than tactile ones. This is due to the fact that single image contains information about a large number of measuring points (> 103), depending on its resolution. In addition, the acquisition of modern cameras and communication interfaces requires just a fractions of a second. This is especially useful when mapping objects with freeform shapes, which by nature cannot be described with single values. Examples of such non-contact digitizing method are presented in Chapter 1.
Freeform surfaces are an essential element of such industries as automotive, aerospace or appliances, and the accuracy of their implementation is often a decisive influence on the efficiency and reliability. With the development of multiaxis machining techniques the number of its applications grows. A consequence of this trend is the need for quality control methods.
In this paper the focus was mainly on applications of optical 3D reconstruction methods in the industrial quality control. Very rapid expansion is observed in this field because of modern trends in production. In part I, the optical 3D reconstruction methods used in quality control will be presented. After this concise characteristics they are compared, and as a result, the method with the greatest potential for applications will be chosen. Perfect candidate appears to be the laser triangulation method which, thanks to the considerable speed and relatively simple components is used successfully for over thirty years to measure the shape of the products on the production lines. Another advantage is its resistance to external light, which is important to reduce other optical and video solutions. Thanks to the use of monochromatic light can be effectively minimized with the use of optical filters.
In the remainder of the work the source of the interference of the laser triangulation are briefly described. From there, one can see that one of the most important disturbances are internal specular reflections that arise while scanning complicated shapes containing highly reflective surfaces. They appear on the triangulation images as multiple light profiles leading to ambiguity. In this case, the 3D model reconstruction is impossible. Because this problem is crucial (it eliminates the triangulation method laser for many parts produced in the metal industry) one can find in the literature several solutions to eliminate the problem of internal reflection. They are briefly characterized in Chapter 4. One of the methods there uses the preliminary scan (pattern) of an object that satisfies the quality criteria, so that the data collected serve as the standard for filtration. Application of non-ideal detail as a golden-template and problems with data synchronization did not allow for the implementation of this concept. It was developed at a time when computer systems were not sufficiently developed to fully exploit it. The wide use of CAD/CAM systems in the modern industry, however, gives new opportunities, so that the use of this approach may be reconsidered. Each product today is manufactured according to the nominal model developed by the designer in the form of a virtual solid model. As applied to quality control, such model can therefore be used as a knowledge base for elimination of gross errors in the process of mapping shape reconstruction. Errors of this type will be in the case of laser triangulation method for example multiple profiles, which formation mechanism is described above.
However, it is not clear whether the use the knowledge of nominal object’s shape will allow for its digital reconstruction in the conditions of strong disturbances associated with surface reflectivity. Because this can be regarded as a measurement method, it is also important to proof if the changes do not derogate from its metrological capacity. Based on the above concepts and concerns a thesis has been formulated together with research tasks. Proof of the thesis requires the test implementation of the modified laser triangulation algorithms and analysis of obtained results. The use of the nominal model for 3D measurements requires extra synchronization-related treatments. Studies in this area have shown that for proper operation of the developed concepts, it is necessary to develop a stable positioning method of the object being analysed, as well as the calibration of the measuring system. They have been described in part II.
Research section (III) describes the verification of the resulting modification of laser triangulation method. In accordance with the thesis its proof requires both the investigation if a new segmentation algorithm eliminates internal reflections, and improves the accuracy of the scan. The first part was carried out using the two examples that manifest very well internal, specular reflections. The first is the v-block, and the other is a shiny freeform surface. Investigations have confirmed the effectiveness of the algorithm. In the second part it was necessary to designate the measuring uncertainty of triangulation setup. The phenomenon of multiple reflection does not, however, manifests in the standard procedure of uncertainty estimation, that requires multiple measurements of gauge blocks. It would therefore be necessary to use more specialized patterns. These, however, significantly impede research carried out under repeatability conditions. A simplified estimation method of measurement’s uncertainty, has been proposed based on the assumption that the segmentation accuracy is one of the components of the uncertainty budget. The convergence of the results of this estimation method and the classic method, argues that the standard assumptions about the immediate impact of the segmentation accuracy on the uncertainty of the measurements. The results suggest that segmentation algorithm improved the ability to detect light profile and, therefore, also contributed to improving the measurement uncertainty.
The last part of the work (IV) summarizes the developed solution and the outcome of the tests.
... In laser triangulation, it is impossible for the stripe to be imaged because of occlusion. Some researchers [9] used another sensor to obtain a second view or project another stripe [10] to reduce the influence of occlusion. A narrower triangulation angel was used to make the system more robust to occlusion [11]. ...
It is very important to acquire accurate depth information of target object or scene for many applications in machine learning. The use of 3D reconstruction based on active laser triangulation technology is very complex in real application. One main problem is that most of these technologies detect light stripes by considering each column or row of the image as independent signals causing lack of robustness. In real application, variable illumination, uneven surface and imaging noise will make stripe detection fail. In this paper, by considering laser stripe distortion assumption, we adopt efficient belief propagation algorithm to extract center of laser stripe, which proves superior to existing peak detection approaches. Because of occlusion and low reflectivity, laser stripe captured by the sensor will be cut into several parts at some points, which are referred to as outliers. As for non-outlier, the SNR of that point is high and the disparity difference between left and right neighbor is slight. First, determine whether a point is an outlier or not by computing the weighted SNR and disparity difference. Then efficient belief propagation algorithm is adopted to infer the outlier map which is called labels in machine learning. Experimental results demonstrate the feasibility of our proposed approach.
... where s is a scale factor. Mavrinac et al. [17] provide the derivation and implementation details of this calibration procedure. ...
... In the experiments, the camera used is the SICK-IVP Ranger E industrial 3D camera with a laser line projector. The camera and laser were mounted and calibrated using two different calibration techniques: laser line calibration [17] and full camera calibration [19]. ...
A method for sensor planning based on a previously developed coverage strength model is presented. The approach taken is known as generate-and-test: a feasible solution is predefined and then tested using the coverage model. The relationship between the resolution of the imaging system and its performance is the key component to perform sensor planning of range cameras. Experimental results are presented; the inverse correlation between coverage performance and measurement error demonstrates the usefulness of the model in the sensor planning context.
In this paper a fast and innovative three-dimensional vision system, having high resolution in the surface reconstruction, is discussed. It is based on a triangulation 3D laser scanner with a linear beam shape. The high precision (few microns) is guaranteed by very small laser line width, small camera pixel-size and proper optical properties of the Telecentric Lens. The entire system has been tested on two kinds of sample objects such as a 20 €cent coin and a set of precision drilling tools. The main purpose of this work is the detection and reconstruction of the 3D surface of tiny objects and the measurement of their surface defects with high accuracy. Furthermore the occlusion problem is faced and solved by properly handling the camera-laser setup. Experimental tests prove the high precision of the system that can reach a resolution of 15 μm.
