3D scanning

OBJECTIVES. The purpose of this preliminary in vitro investigation was to evaluate the accuracy of an intraoral scanner in fully edentulous arches rehabilitated with 6 implants; in this clinical condition it is particularly difficult to ensure sufficient accuracy standards. MATERIALS AND METHODS. For this study a reference metal master model was provided: it had 6 implant analogs inserted to simulate a fully rehabilitated edentulous arch with implants. A scanbody made of PEEK (Polyether Ether Ketone) was inserted in each analog and the positions of each scanbody were calibrated by means of a Coordinate Measuring Machine (CMM). The master model, fitted with the scanbodies and a silicone gingiva, was acquired with the True Definition Scanner (TDS). Several series of scans were taken, each of them consisting of 10 close acquisitions, in order to arrange the calibration of the master model and the series of scans with TDS in the same day. From the mesh of each scan, a segmentation was performed to identify known points referable to both plane and cylinder shapes of the scanbodies. This operation was automatically performed by implementing a dedicated algorithm developed in the Rhinoceros 5.0 software. RESULTS. The results herein are related to one set of 10 acquisitions of the master model. Dimensional analysis assessed the effective diameter of the scanbodies measured by TDS and was compared with the reference diameter measured using a CMM, thus obtaining the dimensional error in the body diameter of the scanbody. The values of dimensional errors varied from a minimum of 15 μm to a maximum of about 39 μm, with standard deviations of up to 9 μm. The location analysis allowed to determine the average location error of the scanbodies centers with respect to the reference positions: they were in a range from 14 to 21 μm, with standard deviations of less than 10 μm. CONCLUSIONS. Within the limitations of this in vitro study, the intraoral scanner under investigation proved to be able to scan a 6 implants full arch with a level of accuracy in line with other data reported in scientific literature, or even with smaller error rates. This level of accuracy is capable of fulfilling the accuracy requirements considered clinically acceptable.

Keywords: Full arch digital impressions , Implants , Intraoral scanner , Scanning dimension errors , Scanning position errors

The present work aims at the numerical prediction of the performance of a Contra-Rotating Propellers (CRP) system for a Remotely Piloted Aerial Vehicles (RPAV). The CRP system was compared with an equivalent counter-rotating propellers configuration which was set by considering two eccentric propellers which were rotating at the same speed. Each contra-rotating test case was built by varying the pitch angle of blades of the rear propeller, while the front propeller preserved the original reconstructed geometry. Several pitch configurations and angular velocities of the rear propeller was simulated. Comparisons showed an improvement of the propulsive efficiency of the contra-rotating configuration in case of larger pitch angles combined with slower angular velocities of the rear propeller.

Keywords: aeronautic propulsion , contra-rotating propellers , frozen rotor technique , OpenFOAM , performance , RPAV

During sintering, porcelain changes its phase composition as well as its physical and mechanical properties. The most evident effect of these transformations is a significant change of shape, which is a combination of shrinkage and pyroplastic deformations, caused by softening. Both of these phenomena are induced by temperature, which is on its turn influenced by several variable factors that are difficult to predict. Especially for products manufactured in large scale, the resulting shape of artefacts may significantly vary even among the same batch. Consequently, for companies demanding high quality standard, this variability entails a high number of rejected products. For this reason, the present work aims at investigating the amount of variation introduced by firing process for an actual industrial product, independently from other (more or less) known variation sources such as the ones related to materials and forming processes. This could help process engineers to focus their attention when trying to improve the quality of final products.

Keywords: Geometric characterization , Porcelain manufacturing , Reverse Engineering , Scattering analysis

An innovative method of tool wear assessment, based on the digitization of the cutting tool performed by a piezoelectric 3D scanner and on the analysis of the surfaces of a 3D model generated using the Reverse Engineering technique, has been developed. To this purpose, face milling experiments were carried out under dry cutting condition on AISI 420 B stainless steel using inserts in cemented carbide, with a two-layers coating (TiN and TiAlN). The time dependence of the insert wear was analysed by interrupting milling at predetermined time values. The proposed approach has been validated by comparing the output provided by the reverse engineering method to that measured experimentally by analysing the worn insert images obtained using a stereo microscope. An excellent agreement between the results given by the two different methodologies has been found. The worn tools have also been analysed using the scanning electron microscopy technique in order to understand the wear mechanisms operating during dry milling.

Keywords: CAD , dry cutting , FEG-SEM , milling process , Reverse engineering , tool wear

This paper presents a multiphysical model of a reversible sleeve air spring to be employed for design and simulation purpose. A multiphysical approach, combining fluid flow with solid mechanics, has been considered to study the interaction between the fluid and the solid structure of the air spring under different pressure conditions. Experimental tests have been developed applying several compression loads to the air spring and measuring the deformation and the reaction force for different values of the initial pressure. An experimental validation has been executed analyzing and comparing the mechanical behaviour of the actual prototype and the virtual model. In particular, the 3D deformation of the air spring has been acquired by means of the Reverse Engineering techniques and the results have been compared with the simulated ones. Moreover, the experimental and simulated air spring vertical stiffness have been matched in order to verify the accuracy of the multiphysical model. The validation procedure demonstrated that the simulation results fitted the experimental ones for different testing conditions.

Keywords: Air spring , CFD , Elastomers , FEM , Mooney-Rivlin model , Multiphysics , Reverse engineering , Structural analysis

3D inspection process is getting more and more interest for manufacturing industries as it helps to carefully check the expected quality of the released products. Much more attention is oriented to optical devices able to quickly capture the whole shape of the product providing many useful information on the process variability and the deliverability of the key characteristics linked to the quality of the product/process. Although the optical control of 3D scanners is mature enough, many factors may influence the quality of the scanned data. These factors may be strictly related to internal elements to the acquisition device, such as scanner resolution and accuracy, and external to it, such as proper selection of scanning parameters, ambient lighting and characteristics of the object surface being scanned (e.g. surface colour, glossiness, roughness, shape), as well as the sensor-to-surface relative position. For the 3D laser-based scanners, the most common on the market, it would be of great industrial interest to study some scanning factors mainly affecting the quality of the 3D surface acquisitions and provide users with guidelines in order to correctly set them so to increase the massive usage of these systems in the product inspection activities. In this context, by using a commercial triangulation 3D laser scanner, the effects of some scanning factors that may affect the measurement process were analysed in the present paper. Working on a sheet metal test part, more complex than the ones commonly used in laboratory and documented in the literature, the scanner-to-object relative orientation and the ambient lighting, as well as an internal scanner parameter, were tested. Through a Design of Experiments (DoE) approach, and setting root mean square error (RMSE) as response function, the outcomes of the tests mainly pointed out that the scanner-to-object relative orientation as well as its position within the field of view of the measurement device are the key factors mostly influencing the accuracy of the measurement process.

Keywords: 3D inspection process , 3D laser scanner , Design of Experiments , Surface acquisition

Polymer-based composites are ideal for applications where high strength-to-weight and stiffness-to-weight ratios are required. In the biomedical field, fiber-reinforced polymers have replaced metals, emerging as suitable alternative. Reverse engineering and additive manufacturing methods are required to achieve the design of customized devices with specific shape and size. At the same time, micro-mechanics and macro-mechanics play an important role in the development of highly functional composite materials. The aim of this research is to develop customized 3D models of a human mandible using reverse engineering, additive manufacturing and composite material technology. Experiments were carried out by loading the models through the condyles and the results show the potential to reproduce the mechanical behavior of a human mandible. Taking into account the curves of the load-arch width decrease, the stiffness of the 3D composite model was 14.1± 1.9 N/mm, which is close to the tested human mandible (17.5 ± 1.8 N/mm).

Keywords: Experimental Testing , Fiber-reinforced composites , Mandible , Reverse Engineering , Stereolithography

Nowadays photogrammetric techniques have known important developments and are widely employed for 3D acquisitions in different fields of application. The paper analyzes the effects of different parameters (texturization, ambient light and water turbidity) on the quality of the 3D reconstruction in underwater photogrammetry. Several experimental tests were performed on a wind turbine blade using a common action camera, the GoPro 4 black edition and a commercial software, Photoscan by ©Agisoft. By means of a DoE (Design of Experiments) approach, 3D models were reconstructed varying the chosen parameters. Each of them was compared with a CAD model, used as reference, obtained by more accurate laser scans VI-9i by Konica Minolta. The results showed that blade texturization, ambient light and water turbidity significantly impact on the quality of the 3D reconstruction. Optimal results were obtained with textured blade, morning ambient light (exposure 1/60, f/2.8 and ISO sensitivity 100) and clear water. Moreover, in order to calculate confidence intervals for regression coefficients, even with few acquisitions, a computer-intensive bootstrap procedure was applied to the regression model. Finally, further confirmation experiments carried out in a deeper swimming pool and with poor conditions (e.g., very low ambient light and no blade texturization) in order to reproduce the real submarine environment. In such situations, an additional source of light and one or more grids, which allow a pattern to be created on the edges of the wind turbine blade, may help reconstructions.

Keywords: Bootstrapping , Design of experiments , Passive no-contact techniques , Reverse engineering , Structure from motion , Underwater photogrammetry

This paper presents a methodology and tools to improve the design of lower limb prosthesis through the measurement of pressure analysis at the interface residual limb-socket. The steps of the methodology and the design tools are presented using a case study focused on a transfemoral (amputation above knee) male amputee. The experimental setup based on F-Socket Tekscan pressure system is described as well the results of some static loading tests. Pressure data are visualized with a colour pressure map over the 3D model of the residual limb acquired using an optical low cost scanner, based on MS Kinect. Previous methodology is useful to evaluate a physical prototype; in order to improve also conceptual design, the Finite Element (FE) Analysis has been carried and results reached so far have been compared with experimental tests. Pressure distributions are comparable, even if some discrepancies have been highlighted due to sensors placements and implemented FE model. Future developments have been identified in order to improve the accuracy of the numerical simulations.

Complete and detailed 3D scanning of cultural heritage artifacts is a still time-consuming process that requires skilled operators. Automating the digitization process is necessary to deal with the growing amount of artifacts available. It poses a challenging task because of the uniqueness and variety in size, shape and texture of these artifacts. Scanning devices have usually a limited focus or measurement volume and thus require precise positioning. We propose a robotic system for automated photogrammetric 3D reconstruction. It consists of a lightweight robotic arm with a mounted camera and a turntable for the artifact. In a virtual 3D environment, all relevant parts of the system are modeled and monitored. Here, camera views in position and orientation can be planned with respect to the depth of field of the camera, the size of the object and preferred coverage density. Given a desired view, solving inverse kinematics allows for collision-free and stable optimization of joint configurations and turntable rotation. We adopt the closed-loop inverse kinematics (CLIK) algorithm to solve the inverse kinematics on the basis of a particular definition of the orientation error. The design and parameters of the solver are described involving the option to shift the weighting between different parts of the objective function, such as precision or mechanical stability. We then use these kinematic solutions to perform the actual scanning of real objects. We conduct several tests with different kinds of objects showing reliable and sufficient results in positioning and safety. We present a visual comparison involving the real robotic system with its virtual environment demonstrating how view poses for different-sized objects are successfully planned, achieved and used for 3D reconstruction.

Keywords: 3D scanning , Automation , Inverse kinematics , Robotic arm , View planning

Nowadays, the creation of methodologies and tools for facilitating the 3D reproduction of artworks and, contextually, to make their exploration possible and more meaningful for blind users is becoming increasingly relevant in society. Accordingly, the creation of integrated systems including both tactile media (e.g., bas-reliefs) and interfaces capable of providing the users with an experience cognitively comparable to the one originally envisioned by the artist, may be considered the next step for enhancing artworks exploration. In light of this, the present work provides a description of a first-attempt system designed to aid blind people (BP) in the tactile exploration of bas-reliefs. In detail, consistent hardware layout, comprising a hand-tracking system based on Kinect® sensor and an audio device, together with a number of methodologies, algorithms and information related to physical design are proposed. Moreover, according to experimental test on the developed system related to the device position, some design alternatives are suggested so as to discuss pros and cons.

Keywords: 3D reconstruction , Blind people , Hand-tracking system , Kinect sensor

In this paper a novel approach, enabling rapid time to market and making shoe collaborative design effectively possible, will be presented. The solution suggested in this work consists of two elements: first, the implementation of a SolidWorks add-on called SYS (SYstem Shoe) whose main goal is to provide a widespread CAD software packages with specific features for shoe design; secondarily the development of a web platform, capable to communicate with and control the SYS add-on. This platform provides the unique opportunity of making the entire system (installed on a server PC) available to external users (small factories concurring to the shoe production chain), without the need of a CAD software own installation. The scenario in which the described system is supposed to work consists of a inter-company network with a main node equipped with the web-CAD platform. This main node acts as a server towards the peripheral nodes (clients: shoe assembly and component-making companies).

Keywords: collaborative design , reverse engineering , Shoe design

Reverse Engineering (RE), also known as "CAD reconstruction", aims at the reconstruction of 3D geometric models of objects/mechanical parts, starting from 3D measured data (points/mesh). In recent years, considerable developments in RE were achieved thanks to both academic and industrial research (e.g. RE software packages). The aim of this work is to provide an overview of state of the art techniques and approaches presented in recent years (considering at the same time tools and methods provided by commercial CAD software and RE systems). In particular, this article focuses on the "constrained fitting" approach, which considers geometrical constraints between the generated surfaces, improving the reconstruction result. On the basis of the overview, possible theoretical principles are drafted with the aim of suggest new strategies to make the CAD reconstruction process more effective in order to obtain more ready/usable CAD models. Finally, a new RE framework is briefly outlined: the proposed approach hypothesizes a tool built within the environment of an existing CAD system and considers the fitting of a custom-built archetypal model, defined with all the a-priori known dimensions and constraints, to the scanned data.

The possibility to realize highly customized orthoses is receiving boost thanks to the widespread diffusion of low-cost 3D printing technologies. However, rapid prototyping (RP) with 3D printers is only the final stage of patient personalized orthotics processes. A reverse engineering (RE) process is in fact essential before RP, to digitize the 3D anatomy of interest and to process the obtained surface with suitable modeling software, in order to produce the virtual solid model of the orthosis to be printed. In this paper, we focus on the specific and demanding case of the customized production of hand orthosis. We design and test the essential steps of the entire production process with particular emphasis on the accurate acquisition of the forearm geometry and on the subsequent production of a printable model of the orthosis. The choice of the various hardware and software tools (3D scanner, modeling software, and FDM printer) is aimed at the mitigation of the design and production costs while guaranteeing suitable levels of data accuracy, process efficiency, and design versatility. Eventually, the proposed method is critically analyzed so that the residual issues and critical aspects are highlighted in order to discuss possible alternative approaches and to derive insightful observations that could guide future research activities.

This paper presents the advancements of an automatic segmentation procedure based on the concept of Hierarchical Space Partitioning. It is aimed at tolerance inspection of electromechanical parts produced by injection moulding and acquired by laser scanning. After a general overview of the procedure, its application for recognising cylindrical surfaces is presented and discussed through a specific industrial test case.

Keywords: Computer aided tolerancing & inspection , Hierarchical space partitioning , Injection moulding , Reverse engineering

This paper presents a novel system that allows product designers to design, experience, and modify new shapes of objects, starting from existing ones. The system allows designers to acquire and reconstruct the 3D model of a real object and to visualize and physically interact with this model. In addition, the system allows designer to modify the shape through physical manipulation of the 3D model and to eventually print it using a 3D printing technology. The system is developed by integrating state-of-the-art technologies in the sectors of reverse engineering, virtual reality, and haptic technology. The 3D model of an object is reconstructed by scanning its shape by means of a 3D scanning device. Then, the 3D model is imported into the virtual reality environment, which is used to render the 3D model of the object through an immersive head mounted display (HMD). The user can physically interact with the 3D model by using the desktop haptic strip for shape design (DHSSD), a 6 degrees of freedom servo-actuated developable metallic strip, which reproduces cross-sectional curves of 3D virtual objects. The DHSSD device is controlled by means of hand gestures recognized by a leap motion sensor.

Objective: To define and validate a method for the measurement of 3-dimensional (3D) morphometric parameters in polygonal mesh models of canine femora. Study Design: Ex vivo/computerized model. Sample Population: Sixteen femora from 8 medium to large-breed canine cadavers (mean body weight 28.3 kg, mean age 5.3 years). Methods: Femora were measured with a 3D scanner, obtaining 3D meshes. A computer-aided design-based (CAD) software tool was purposely developed, which allowed automatic calculation of morphometric parameters on a mesh model. Anatomic and mechanical lateral proximal femoral angles (aLPFA and mLPFA), anatomic and mechanical lateral distal femoral angles (aLDFA and mLDFA), femoral neck angle (FNA), femoral torsion angle (FTA), and femoral varus angle (FVA) were measured in 3D space. Angles were also measured onto projected planes and radiographic images. Results: Mean (SD) femoral angles (degrees) measured in 3D space were: aLPFA 115.2 (3.9), mLPFA 105.5 (4.2), aLDFA 88.6 (4.5), mLDFA 93.4 (3.9), FNA 129.6 (4.3), FTA 45 (4.5), and FVA −1.4 (4.5). Onto projection planes, aLPFA was 103.7 (5.9), mLPFA 98.4 (5.3), aLDFA 88.3 (5.5), mLDFA 93.6 (4.2), FNA 132.1 (3.5), FTA 19.1 (5.7), and FVA −1.7 (5.5). With radiographic imaging, aLPFA was 109.6 (5.9), mLPFA 105.3 (5.2), aLDFA 92.6 (3.8), mLDFA 96.9 (2.9), FNA 120.2 (8.0), FTA 30.2 (5.7), and FVA 2.6 (3.8). Conclusion: The proposed method gives reliable and consistent information about 3D bone conformation. Results are obtained automatically and depend only on femur morphology, avoiding any operator-related bias. Angles in 3D space are different from those measured with standard radiographic methods, mainly due to the different definition of femoral axes.

In the last decade, sandwich composite materials have had an increasing use in design of racing boats. The main reasons are: higher strength-weight ratio, low density, excellent durability and versatility. The knowledge of impact response is very important to design racing boats. The aim of the present study is the investigation of absorbing impact energy ability of a sandwich composite material used for offshore vessels in UIM (Unione Internationale Motonautique) Championship. The material analysed in this study is a sandwich manufactured with hand lay-up technique. In the first phase, the damage assessment of single impact has been studied with an optical measurement technique. In a second phase, the damage evaluation due to repeated impacts has been analysed with the similar technique.

Keywords: Damage accumulation , Lightweight composites , Low energy impact , Nautical applications , Optical mesaurements , Safety design

The present work collects some results of the three-years Research Program "BioForming", funded by the Italian Ministry of Education (MIUR) and aimed to investigate the possibility of using flexible sheet forming processes, i.e. Super Plastic Forming (SPF) and Single Point Incremental Forming (SPIF), for the manufacturing of patient-oriented titanium prostheses. The prosthetic implants used as case studies were from the skull; in particular, two different Ti alloys and geometries were considered: one to be produced in Ti-Gr23 by SPF and one to be produced in Ti-Gr2 by SPIF. Numerical simulations implementing material behaviours evaluated by characterization tests were conducted in order to design both the manufacturing processes. Subsequently, experimental tests were carried out implementing numerical results in terms of: (i) gas pressure profile able to determine a constant (and optimal) strain rate during the SPF process; (ii) tool path able to avoid rupture during the SPIF process. Post forming characteristics of the prostheses in terms of thickness distributions were measured and compared to data from simulations for validation purposes. A good correlation between numerical and experimental thickness distributions has been obtained; in addition, the possibility of successfully adopting both the SPF and the SPIF processes for the manufacturing of prostheses has been demonstrated.

Cranioplasty is a surgery in which a prosthesis must be anchored on skull bone to repair a defect. One of the most used materials is the titanium. However, titanium prostheses could be made using the incremental sheet forming (ISF). Since titanium and bone are characterized by different Young modules, a detailed design of anchoring system is required to avoid cranial rupture. Aim of this study was to present a design procedure in order to identify the optimal anchoring system in case of craniofacial prostheses made with ISF. In detail, an optimization process and a predictive model for bone stress were used, choosing the numerical outputs of different FEM analyses as input data. The results indicate that our predictive and optimization models are accurate and, so, that this procedure could be very helpful for the prosthesis design, as demonstrated by the application of the procedure to a real case study.

Keywords: Anchoring system , Design procedure , Incremental sheet forming , Titanium prosthesis