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Source publication
Purpose
Investigate the use of two imaging‐based methods – coded pattern projection and laser‐based triangulation – to generate 3D models as input to a rapid prototyping pipeline.
Design/methodology/approach
Discusses structured lighting technologies as suitable imaging‐based methods. Two approaches, coded‐pattern projection and laser‐based triang...
Context in source publication
Context 1
... generation of 3D CAD models is usually the first step in a rapid prototyping (RP) system (Chua et al. , 2003; Asiabanpour and Khoshnevis, 2004; Ding et al. , 2004; Li et al. , 2002; Song et al. , 2002). Additionally, CAD modeling is often the most time-consuming part of the entire RP chain (Chua et al. , 2003). Figure 1 depicts the RP process chain and illustrates where CAD modeling fits into this chain. The traditional approach to CAD modeling is through engineering drawings. A designer inputs dimensions and interconnects lines (along with other basic shapes) using CAD software to create a virtual 3D model. This CAD model serves as the starting point of the RP process chain. In this paper, we present an alternative to this CAD modeling through the use of 3D scanning technology known as structured lighting. We specifically explore two methods of structured lighting – coded pattern projection and laser triangulation – as potential approaches. As Figure 1(a) shows, the CAD model is first converted typically into a stereolithography (STL) file and then pre-processed to verify the STL specification and sliced into cross sections. Next, the pre-processed files drive the automated building through technologies such as selective layer sintering, stereolithography, or layered object manufacturing. Finally, the RP chain moves to post-processing, which consists of cleaning to remove excess parts or residual resin, curing to account for pockets of embedded liquids, and finishing to improve aesthetics. Our area of emphasis for this paper in this pipeline is the initial CAD model generation. This initial step requires accurate models of the object of interest that are suitable for the STL files that drive the prototyping process. An emerging method for CAD generation is 3D scanning technology from the field of machine vision. Traditionally, machine vision (also known as computer vision) has not played a major role in manufacturing or prototyping. The introduction of solid-state and low-cost imaging devices however, has led to increased accuracy and faster data acquisition. Thus, imaging-based solutions are becoming attractive to incorporate into RP. Figure 1(b) demonstrates incorporating 3D scanning into the RP chain. Here, we have replaced the CAD modeling step with 3D scanning to generate a model of an existing real-world object. This 3D scanning is similar to coordinate measuring machine (CMM) technologies that capture 3D point measurements of surfaces. CMM are a mature and established technology within current manufacturing environments. The CMMs typically use a touch probe that navigates (either manually or automatically) around the surface of an object collecting data point measurements. The difference of the methods in this paper relative to CCM is that we employ imaging-based methods – specifically structured lighting techniques – rather than the touch-probe methods of CMM. CMM require path planning for probe placement (often a complex process for complicated objects), and the mechanical dynamics of the probe constrain the scan speed of collecting data. Additionally, CMM require the probe to physically touch – or at least come within close proximity to – the surface under measurement. This physical contact is usually not a major issue, but the probe can damage the surface with errors in path planning under certain conditions. Imaging-based approaches, on the other hand, offer potential for faster data collection using solid-state sensors and offer a stand- off approach to measurements, but the drawback is that imaging- based systems currently have reduced accuracy relative to CMM techniques. Fortunately, as semiconductors continue to improve – respective to Moore’s Law – the accuracy of imaging-based scanners will continue to improve as well. Within the past decade, this trend has seen movement from centimeter to sub-millimeter accuracy. We expect this trend to continue. The addition of 3D scanning to the RP process chain enables important capabilities. A situation that might arise in RP is the need to modify an existing part, which may be outdated or have field modifications. With an outdated part, CAD models may not exist or they may no longer be accessible. The original manufacturer of the part may have gone out of business, for example, or the CAD models may have been lost or discarded. With field modifications, a lack sufficient support from the original CAD models becomes a problem. A technician in the field may have found a better way to mount the part by modifying the original design, or damage to the part may require a modification to correct the damage. This modification may not be documented in the CAD archives. Also, a design engineer may seek to introduce a value-added design to an existing part, but the original manufacturer of the part may not be willing to release their internal CAD files for proprietary reasons. The process of 3D scanning overcomes these problems by allowing the creation of a CAD model by scanning the existing object. The potential for imaging-based approaches over more mechanical solutions, i.e. CMM systems, is that imaging scanners offer increased scanning speeds and enable more automation in the scanning process. A CMM touch probe collects only a single data point with each measurement. By contrast, imaging-based scanners collect a set of data points where, the size of the set is dependent on the scanning technology but typically ranges from 256 points to over 100,000 points. These large data sets yield large speed benefits. For increased automation, imaging-based scanners leverage many techniques from the field of computer vision for data registration, integration, and visualization. Although many of these techniques are applicable to both CCM and imaging systems, the natural problem domain is more readily developed with the imaging-based systems. Thus, these computer vision algorithms enhance the automation potential. Imaging-based 3D scanners acquire measurements by capturing images of an object and then reconstructing 3D models from those images. The scanner is positioned at various viewing angles to fully cover each surface of the object, and this ensemble of data sets leads to the reconstructed 3D CAD model. We typically refer to the measurements from 3D scanners as range images where each pixel of such images represent the distance (or depth) from a given scanner location to each of the surface points on the object (Besl, 1989). A classification of various methods for generating 3D data from objects appears in Figure 2 with emphasis on the imaging methods to include subcategories. The most well-known method of 3D range image acquisition is passive triangulation, also known as stereo vision. Stereo vision involves coordinating two cameras to generate depth information about a scene by automatically finding corresponding features in both stereo images. The correspondence problem is ill-posed and therefore leads to either sparse distance measurements or erroneous results caused by mismatches. As an alternative to passive stereo, active stereo systems such as structured lighting systems offer more robust methods of measurement (Bernardini et al. , 1999). (As a side note, some authors use the term active stereo to also refer to the case where two intensity cameras are used – as in our definition of passive stereo – but these cameras are “actively” controlled to either pan or tilt synchronously, or to change their baseline. We mention this definition for clarity as our definition for active stereo uses a single camera with an active light source.) In the next two sections that follow, we discuss in more detail two particular structured lighting methods that are applicable to the RP problem. The first method is a coded-pattern structured lighting system that uses a camera along with a pattern projector. The second method is a laser-based method that also uses a single camera but rather than a pattern project uses a laser for the active light source. For each of these methods, we specifically focus on two commercial products as implementations of these methods. Coded-pattern projection scanners project a known light pattern, or set of coded patterns, onto the surfaces of an object. The light pattern follows the contours and shape of the object. Figure 3 illustrates an example of the projection of a light pattern onto an automotive water pump. Notice that the shape of the pump distorts the pattern as viewed by the camera. In a limited sense, this distortion leads to the recovery of 3D information based on triangulation and projective geometry. The principle of this 3D recovery is through triangulation calculations (Geng, 1996). Figure 4 illustrates this triangulation geometry. When the distance between two points and the angle from each of these points to a third point are known, the coordinate of the third point can be calculated by the following ...
Citations
... Data acquisition methods for burr measurement[9] ...
One of the major issues of drilling operations pertains to the formation of burrs, which greatly influences the accuracy of the manufactured parts, and, thus, the capability to meet the desired performance of the part. To remove or prevent these burrs, their geometry must be measured accurately, even though they are sharp and irregular in shape. The accurate measurement of the geometry of a burr will lead to the development of a proper deburring method. In this work, the authors describe a simple and convenient new measurement technique for drilling burr profiles and a developed drilling burr measurement system based on surface area. The new method presented in this research aims at providing a comparative evaluation of the height, arc length and area of the burr, as well as its geometrical characteristics. When the average height and arc length measurement methods are compared with the area measurement method, large deviations in burr height are detected. In particular, these deviations increase more in non-uniform burrs. In the measurement of burr size, the new developed method is based on area measurement and is carried out using a computer. Therefore, there is no deviation between the measurements. In contrast, the average deviation ranges for the height and arc length measurement methods are found to be 9.94–48.14% and 6.07–18.82%, respectively.
... Combined with the advantages of SFS and 3D morphable model (3DMM) methods, they proposed an error evaluation method based on linear optimization for fusion of geometric and surface normal errors, which improved the accuracy and efficiency of 3D model reconstruction to some extent. 20,21 The disadvantage of 3DMM algorithm is that it needs a priori 3D face database information, and the reconstruction process is computationally expensive and time-consuming. 22 In addition, although the 3DMM method has a good global accuracy, the reconstruction accuracy of some detail areas highlighting face characteristics is not ideal. ...
With the development of computer technology and three-dimensional reconstruction technology, three-dimensional reconstruction based on visual images has become one of the research hotspots in computer graphics. Three-dimensional reconstruction based on visual image can be divided into three-dimensional reconstruction based on single photo and video. As an indirect three-dimensional modeling technology, this method is widely used in the fields of film and television production, cultural relics restoration, mechanical manufacturing, and medical health. This article studies and designs a stereo vision system based on two-dimensional image modeling technology. The system can be divided into image processing, camera calibration, stereo matching, three-dimensional point reconstruction, and model reconstruction. In the part of image processing, common image processing methods, feature point extraction algorithm, and edge extraction algorithm are studied. On this basis, interactive local corner extraction algorithm and interactive local edge detection algorithm are proposed. It is found that the Harris algorithm can effectively remove the features of less information and easy to generate clustering phenomenon. At the same time, the method of limit constraints is used to match the feature points extracted from the image. This method has high matching accuracy and short time. The experimental research has achieved good matching results. Using the platform of binocular stereo vision system, each step in the process of three-dimensional reconstruction has achieved high accuracy, thus achieving the three-dimensional reconstruction of the target object. Finally, based on the research of three-dimensional reconstruction of mechanical parts and the designed binocular stereo vision system platform, the experimental results of edge detection, camera calibration, stereo matching, and three-dimensional model reconstruction in the process of three-dimensional reconstruction are obtained, and the full text is summarized, analyzed, and prospected.
... Data processing, as a second phase, is referred to an image processing which includes in rough steps building of sparse point cloud, building dense point cloud and building polygonal mesh model [24][25][26], while obtained measurement results from CMM (point cloud) go directly to building the polygonal mesh model [27,28]. ...
... Rapid development of three-dimensional (3D) technologies has enabled their integration in different fields of application, such as biomedicine [1,2], dentistry [3], gaming industry [4], automotive industry [5], cultural heritage [6], civil and architectural engineering [7], etc. 3D technology presents a very general term and it can be defined as technology that aims to create virtual or physical 3D models using computers and other devices that support data processing in digital form [8]. Artists, now surrounded by 3D technology, can facilitate and improve their artwork by using them. Based on 3D technologies in this field digital sculpting was born. ...
Nowadays 3D technologies are integrated into all aspects of modern lives. This integration of 3D technologies paved new paths for further expansion of other fields, most recently the field of arts. In this paper bridging the symmetry-related gap between physical and digital sculpting by application of reverse engineering modeling was presented. This approach enables artists to express their art in physical 3D object form and then transfer it into a digital world in order to satisfy various prerequisites (here, the final 3D model is to be ideally symmetrical). In order to describe this process, one case study is selected. With the use of close-range photogrammetry based on structure from motion, as a 3D digitization technique, a physical 3D model of a human head - manually sculpted in clay was digitized. In order to obtain a final physical or digital 3D model of sculpted head and to make it symmetrical, the symmetry analysis and correction was performed. Namely, by comparing digitized 3D model with its idealized 3D model (that was created based on symmetry-correction), symmetry analysis was carried out using computer-aided inspection. The results showed critical regions of the physical i.e. its digitized 3D model that, because of having no acceptable levels of dimensional deviations (regarding ideal symmetry), it must be corrected/minimized. This can be performed either by manual re-sculpting of the physical 3D model, or by modification of digitized 3D model (if there is no intention to use idealized 3D model for subsequent CNC-fabrication as an example).
... Low-cost systems developed by using off-the-shelf hardware as webcam, projectors, etc., give additional opportunities to gather 3D information for further use in different applications. They can be used in cultural heritage documentation [1], [2], [3], [4], [5], human body parts [6], [7], [8], [9], or full body [10], [11], creating CAD models of mechanical parts, [12], [13], industrial rubber parts [14]. Photogrammetry is another technique for object digitalization: it creates 3D models form 2D images taken in 360 o , with overlapping parts of the images. ...
Engineers in different areas of production increasingly use 3D scanning techniques, where speeding up the development process is one of the key factors for being competitive in today’s market. Virtualizations of physical objects, to recreate parts where drawing or CAD data are missing, or making changes to the exist-ing one is one of the main uses. From a wide range of commercial scanners used for digitalization, 3D low-cost scanning systems have gained a high interest.
The aim of this paper is to show the implementation of two low cost scanning systems for creating digital replicas of mechanical parts. The process of digital data acquisition, processing and creating 3D virtual models will be presented. A good implementation of light conditions, sensor type/size of digital camera in photogrammetric system can achieve high Level Of Detail (LOD) compared with structured light system. The displacement map generated from texture increase the resolution geometry details as accurately as possible. Also for small parts photogrammetry is more flexible.
... (ii) Range-based modeling. The 3D object's detailed geometric information is acquired directly in this modeling method, which relies on artificial lighting, such as the structured light [76,63], coded light [100,143], and laser light [26,208]. The techniques are based on triangulation, timeof-flight, continuous wave, and interferometry reflectivity measurement principles. ...
This paper reviews the state-of-the-art methodologies for developing computer-aided design (CAD) model based systems for assembly simulation, planning and training. Methods for CAD model generation from digital data acquisition, motion capture, assembly modeling, human–computer interface, and data exchange between a CAD system and a VR/AR system are described. Also presented is an integrated methodology for designing, planning, evaluating and testing assembly systems. The paper further describes the implementation of these methods and provides application examples of CAD model based simulation for virtual assembly prototyping, planning and training. Finally, the technology gaps and future research and development needs are discussed.
... "zakładki". Po zakończeniu tego procesu konieczne jest przekształcenie wynikowego zbioru punktów w bryłę [65,66]. Najprostszym rozwiązaniem jest skorzystanie z algorytmu triangulacji, pozwalającego na wygenerowanie pliku w formacie STL, będącego zapisem chmury, w której każdy punkt jest połączony z najbliższymi sąsiadami trójkątnymi płaszczyznami. ...
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.
... A binary file stores the topological information in a 32-bit single floating-point format, while the ASCII file stores the information as ASCII strings, with keyword strings as indicators. Though the size of the ASCII STL format is larger than the one of the binary format, it is human readable (Alves, 2006;Alves and Bártolo, 2006;Chen et al., 1999;Page et al., 2005). Commercial equipments present working areas ranging from 70 £ 70 mm to 110 £ 110 mm and similarly to a conventional machining centre, are equipped with three linear axes, X, Y, Z with the possibility of adding rotational axis A and/or C (Figure 1). ...
Purpose
Laser milling is a non‐conventional layer‐by‐layer material removal technology suitable for machining a wide range of materials. This technology is particularly suitable to produce microstructures inside cavities, also obtained by other conventional processes, though with larger material removal rates, or for the direct development of microcavities not requiring high removal rates. This paper seeks to evaluate the capacity of laser milling for manufacturing of mould inserts.
Design/methodology/approach
The paper examined several specific features of laser milling, important for the manufacturing of mould inserts, such as walls verticality, unselected illuminating areas, due to an incorrect STL removal volume definition, aspiration process and orientation, to prevent welding of re‐solidified particles on the surface. Two mould inserts were produced too, assembled on a metallic mould frame and tested with different injection conditions.
Findings
The findings suggest that laser milling is a suitable technology to produce small mould insert for injection moulding, though injection conditions are different as one moves from macroscopic to microscopic injected parts. New design guidelines must be undertaken jointly with the assessment of laser milling performance to make mould microcavities. One of the major difficulties of this process is to keep the side walls vertical plus the generation of undesirable machined volumes, due to unselected illuminating areas below the STL volume, corresponding to the volume to be removed, whenever laser milling is used to operate with structures previously machined. To prevent welding of re‐solidified particles on the surface a proper aspiration must also be considered.
Originality/value
The paper describes the benefits of laser milling technology.
... In a modern literature there is not much work, which would describe a laser scanning process on an input/output process box basis. There are many contributions which investigate usually one or two parameters and their influence on a quality (precision) of laser scann results [1,2,3], but there are practically no scientific investigations which would describe a process as a whole, taking into account wide range of crucial parameters and their mutual interactions, and moreover there are very few attempts of optimizing those factors [ 4 ], or even less to predict them. There are a few good accesses which investigated the influence of free form surface lean angle and distance of laser head from scanned object on quality of reconstructed surface [5,6], but we seriously believe that in order to establish a reliable model of scanning process, at least the mayority of most important possible input scan parameters should be considered. ...
In presented paper a design model is developed which is used to find an optimal design space in order to improve precision and accuracy of reversed 3D models. Significant parameters and their mutual effects in scanning process are recognized with the help of Design of Experiments (DOE) principles, and in second step recognized significant parameters are also optimized using the RSM (Response Surface Methodology). Back propagated neural network is used for prediction of response factors whose input variables are not possible to set during experimentation due to the nature of the scan device. With neural network (NN) predicted response-design data, the Analysis of Variance (ANOVA) test was performed. On a basis of significant parameters the analytical model is established, which enables prediction and optimization of critical scan parameters, according to the prescribed standard deviation (abberation) of analysed 3D CAD models. After getting knowledge about the relationships between significant parameters it is possible to predict and optimize them using a model established in the RSM on a basis of D-optimal Design of Experiment test (DOE). At the end also the precision assessment of predicted response factors by DOE approach and by neural network approach is done and results are beeing compared.
... Acquisition systems can be divided into several hierarchical groups as shown in Fig. 2. Imaging-based scanners have become very popular for RE, and they have been investigated for several years. See Page et al., 4 Li et al. 2 and Peng et al. 5 Their main advantage with respect to the tactile methods such as CMM is that they are faster and allow quasi real-time data acquisition. See Rusinkiewicz et al. 6 (a) Figure 3. ...
The purpose of this research is to investigate imaging-based methods to reconstruct 3D CAD models of real-world objects. The methodology uses structured lighting technologies such as coded-pattern projection and laser-based triangulation to sample 3D points on the surfaces of objects and then to reconstruct these surfaces from the dense point samples. This reverse engineering (RE) research presents reconstruction results for a military tire that is important to tire-soil simulations. The limitations of this approach are the current level of accuracy that imaging-based systems offer relative to more traditional CMM modeling systems. The benefit however is the potential for denser point samples and increased scanning speeds of objects, and with time, the imaging technologies should continue to improve to compete with CMM accuracy. This approach to RE should lead to high fidelity models of manufactured and prototyped components for comparison to the original CAD models and for simulation analysis. We focus this paper on the data collection and view registration problems within the RE pipeline.
