Geometric modeling and processing

In the present work, sheet-forming processes, i.e. super plastic forming and single-point incremental forming, have been adopted for the manufacturing of custom prostheses, instead of subtractive and additive techniques that are time- and cost-consuming for a single-piece production. Regarding concerns of the material, three different titanium alloys were used: pure titanium and two grades of the alloy Ti-6Al-4V (the standard one and the extra low interstitial one). Since no standard protocol exists to assess the mechanical performance of cranial implants, an experimental procedure has been designed and used in this work for producing polymethylmethacrylate supports, on which the cranial prostheses were firmly connected and subjected to impact puncture tests (drop tests). An experimental campaign could thus be conducted to investigate the effect on the mechanical response of (a) the titanium alloy, (b) the initial blank thickness and (c) the manufacturing process. Drop tests, carried out according to the proposed procedure, have shown no failure of the prostheses, neither in the area of the impact nor in the anchoring region and have revealed that, irrespective of the adopted manufacturing process, which does not alter the material, the amount of energy absorbed by the implants is always larger than 70%.

Keywords: Drop test , Pure titanium , SPF , SPIF , Ti-6Al-4V , Ti-6Al-4V-ELI

Considering the progressively expansive trade world, "time to market" of productions and goods has turned into a key element for business accomplishment. There are diverse practices that antedate design faults and unveil products on the market in minus time. Among the most used methods in the design and explanation of the necessities, quality function deployment (QFD) and design for Six Sigma (DFSS) can be used. In the prototyping stage, it is probable to address the emergent technology of additive manufacturing. Today, 3D printing is employed as a quick prototyping technique. Nevertheless, the tangible task which industry is fronting is the adoption of these machines for large-scale production of components, which is now possible with new HP multi fusion. The goal of this paper is to illustrate the entire product development process taking advantage of the most modern models and technologies for the final realization of a case study that involves the design and prototyping of an innovative multifunctional fan (lamp, aroma diffuser, and fan) through the multi jet fusion of HP. To begin with, issues related to the DFSS, the QFD and their application to identify the fan requirements are explored. Once the requirements have been defined, the modern CAD design systems and the CAE systems for the validation of the case study will be analyzed and applied. Finally, HP's multi jet fusion methodology and design rules for additive manufacturing will be analyzed in detail, trying to exploit all the positive aspects it offers.

Keywords: CAD , CAE , Design for additive manufacturing , Design for Six Sigma , FEA , Multi jet fusion , Product development , QFD , Rapid prototyping

Over the last years, good strategies for efficient manufacturing were considered increasing the volume of production and reducing the time and costs. Emerging design strategies as the Design for Environment and life cycle assessment, the Design for Sustainability, the Design for Disassembly moved the focus to conceive a product by taking care of all the effect that its use can cause to the economy, to the society and to the environment, also at its disposal. In this context, design strategies have to be enhanced in order to integrate innovation with sustainability and social care. Thus, the horizon for strategic manufacturing has to pay particular attention to the effects that it could produce to the surrounding environment. This way, some manufacturing techniques that could be considered obsolete in terms of sustainability awareness, but that are not yet ready to be replaced by advanced available technologies, need a requalification in order to be collocated in the current scenario. In this paper, the open moulding technique has been discussed in order to update the current manufacturing technique to meet the emerging sustainable strategies. Through the integration of QFD and TRIZ an innovative design method have been assessed to enhance the manufacturing process by means of computer aided engineering devices. PrinterCAD is a project that aims to manage additive and subtractive techniques, applied to complex and large-scale products, by means of an open source software with an integrated module, in order to enhance the CAD, CAM and slicing for the 3D printer's languages intercommunication.

Keywords: CAD , CAM , Hybrid manufacturing , Open source , QFD , TRIZ

Feature-based modeling and feature recognition algorithm are state of the art technologies, mainly used to favor the integration and exchange of data between design and manufacturing phases. This paper aims to investigate the possibility to extend the use of the feature recognition as a means for the prevention of ergonomics issues during the manual assembly phase, such as Work-related Musculo-Skeletal Disorders (WMSDs). Starting from the features analysis of a 3D product model, the proposed five steps method allows preventively identifying potential ergonomics issues. The main novelty of this study is related to the correlation between design tools, product virtual representations (e.g. 3D models), assembly and ergonomics aspects. Results obtained with two case studies, a cooker hood and a tool-holder carousel, confirm the usefulness of the proposed method in helping designers to prevent potential ergonomics issues for operators involved in the assembly phase.

Keywords: Ergonomics , Feature recognition , Manual assembly , Virtual product model , Work-related Musculoskeletal Disorders

Versatile, cheap and non-invasive 3D acquisition techniques have received attention and interest in the field of biomedicine in recent years as the accuracy of developed devices permits the acquisition of human body shapes in detail. Interest in these technologies derives from the fact that they have the potential to overcome some limitations of invasive techniques (CT, X-rays, etc.) and those based on 2D photographs for the acquisition of 3D geometry. However, the data acquired from the 3D scanner cannot be directly used but need to be processed as they consist of 3D coordinates of the acquired points. Therefore, many researchers have proposed different algorithms which recognise the shape of human body and/or its features when starting from a 3D point cloud. Among all possible human body features to be evaluated, symmetry results the most relevant one. Accordingly, this survey systematically investigates the methods proposed in the literature to recognise 2D symmetry by the symmetry line and bilateral symmetry by the symmetry plane. The paper also analyses qualitative comparisons among the proposed methods to provide a guide for both practitioners and researchers.

Keywords: 3D scan , Digital human model , Symmetry line , Symmetry plane

The design of gas turbine ventilation systems (VSs) is a lengthy and tedious process, often requiring weeks to refine a single design concept and by additional time to manufacture it. This is particularly true when dealing with structural design since the typical approach followed by main worldwide manufacturing companies is to outsource finite elements analysis and, often, the 3d modelling phase itself. Moreover, the structural design process is iterative: the modeling and finite elements analysis steps are repeated several times whenever a new VS has to be produced. Accordingly, speeding-up the structural design phase is today a crucial issue for gas turbine sector. Keeping the above objective in mind, the present paper proposes a CAD-based tool, implemented in a commercial 3D CAD software package (SolidWorks), supporting and partly automating the complex structural VS design process. The solution suggested in this work consists of the design and implementation of a SolidWorks add-in, called DuctWorks, developed by using C# programming language. Differently from commercially available solutions, the proposed tool is specifically thought keeping in mind the necessity of performing a final structural assessment, which is of utmost importance given the considerable dimensions and stresses this kind of VS are subject to in the specific field of GT and energy production industry. Tested against a set of case studies, DuctWorks proved to be effective in allowing designers to accelerate the ventilation systems design process with excellent results when compared with the traditional design process.

Keywords: CAD tools , FEA , ventilation system

The standard treatment for bones fractures entails the use of a tailor-made plaster cast which has several disadvantages: its weight generally causes discomfort, it cannot be taken off without breaking it, it can cause skin rashes and prevents ventilation of the treated area. Therefore, the application of traditional casts to orthopaedics patients does not represent, to date, the best option. To overcome the above-mentioned drawbacks, many strategies based on reverse engineering and additive manufacturing techniques have been proposed and proved to be a valid alternative for producing custom orthoses. Encouraged by the aforementioned results, the authors have developed a low-cost system (called Oplà), specifically dedicated to the hand-wrist-arm district of paediatric patients and capable of creating a 3D CAD model of the orthosis ready to be printed by using additive manufacturing techniques. Such a system comprises a 3D scanner, a control software and a semi-automatic CAD procedure to easily model the orthopaedic device on each patient, without the need of CAD modelling professionals. To evaluate if Oplà can be effectively used by the medical staff to design patient specific 3D printable orthoses in the clinical practice, a preliminary usability assessment has been performed. Five professional nurses from the Meyer Children's Hospital of Florence (Italy) have been selected and trained in the use of the system. Subsequently, each of them has been asked to perform the whole process for the same patient. Effectiveness, efficiency and satisfaction have been measured in accordance to ISO 9241-11. Results proved that the Oplà system is characterized by a good usability allowing the user to easily and intuitively perform all the tasks in a reasonable time.

Keywords: CAD , Cast modelling , Reverse engineering , Usability

Given a to-be-watermarked 3D model, a transformed domain analysis is needed to guarantee a robust embedding without compromising the visual quality of the result. A multiresolution remeshing of the model allows to represent the 3D surface in a transformed domain suitable for embedding a robust and imperceptible watermark signal. Simplification of polygonal meshes is the basic step for a multiresolution remeshing of a 3D model; this step is needed to obtain the model approximation (coarse version) from which a refinement framework (i.e. 3D wavelet analysis, spectral analysis, …) able to represent the model at multiple resolution levels, can be performed. The simplification algorithm should satisfy some requirements to be used in a watermarking system: the repeatability of the simplification, and the robustness of it to noise or, more generally, to slight modifications of the full resolution mesh. The performance of a number of software packages for mesh simplification, including both commercial and academic offerings, are compared in this survey. We defined a benchmark for testing the different software in the watermarking scenario and reported a comprehensive analysis of the software performances based on the geometric distortions measurement of the simplified versions.

Keywords: 3D watermarking , Mesh comparison , Mesh simplification , Wavelets 3D

The visualization and analysis of mosaics and pavements are often compromised by their large sizes, which do not enable the observer to perceive their whole arrangement or to focus on details placed in farthest areas from its boundaries. Moreover, the usual precarious state of conservation of these artefacts, often with damaged or missing areas, makes it difficult to perceive their original aesthetic value. To overcome these limitations, we propose an application of augmented reality able to support the observer in two ways: first, the application completes the missing surface of the mosaic or pavement by integrating the existent surface with a virtual reconstruction; second, it enables the analysis of the geometric pattern of the mosaic/pavement by overlaying virtual lines and geometric figures in order to explicit its geometric arrangements. The result is achieved via a custom Android application able to recognize and track the mosaic figure pattern and extra marker board, obtaining in that way a coordinate system used to render in real-time the reconstruction of the mosaic. Such rendering is overlaid to the video stream of the real scene. The application runs on a standard smartphone embedded in a Google Cardboard-compatible viewer and therefore is extremely affordable. As a case study, in order to reconstruct its aspects and to analyse its geometric pattern, we chose the roman mosaic re-found in Savignano sul Panaro (near Modena, Italy) in 2011, after 115 years from its first discovery, which is preserved less than half of its original 4.5 x 6.9 m surface.

Keywords: Augmented Reality , Cultural heritage , Geometric pattern , Photogrammetry , Real-time visualization , Roman mosaic

This paper proposes the integration of photogrammetric reconstruction, 3D modelling and augmented reality application in order to achieve the complete visualization of a stone sculpture even if highly damaged or fragmentary. The first part of the research aims to the reconstruction of the original aspect of an incomplete sculpture, by using photogrammetry techniques based on standard resolution photos and free software in order to obtain a first model; then, we integrate this model with other 3D digital data (from other sculptures of the same period) or with 3D modelling based on historical sources and views from historians, aiming to achieve the original aspect of the sculpture. The second part of the research consists of the embedding of the obtained model in a custom application able to render in real-time the 3D reconstruction of the lion. Then, the rendering is overlaid to the video stream of the real scene and, as a result, a complete 3D digital model of the sculpture is achieved and could be visualized through a VR viewer. As a case study, we focus on a Roman stone sculpture of a male lion conserved in the Museo Estense of Modena (Italy), which lacks of its head and its four legs. The original aspect of the lion may be achieved by integrating the damaged sculpture with other photogrammetric reconstructions of lions sculptures of the same period and with 3D model based on historical sources. Finally, the lion is visualized through an augmented reality application which digitally overlays the reconstructed models on the original one.

Keywords: Augmented Reality , Cultural heritage , Photogrammetry , Real-time visualization , Virtual modeling

This paper deals with a numerical investigation, based on the Finite Element (FE) theory, of a Structural Health Monitoring (SHM) system for a large radio-telescope, aimed to damage detection and location. The investigated SHM system is based on the comparison of the Frequency Response Functions (FRFs) achieved under both pristine and damaged configurations, respectively. A preliminary study has been carried out in order to achieve information on the optimal sensors locations. As a result, the structural response of the radio-telescope under the in-service loading conditions has been numerically investigated. All FE analyses have been carried out by means of MD Nastran® code.

Keywords: Damage , FE Analysis , Modelling , Radio-Telescope , SHM

Manual Material Handling (MMH), by pushing or pulling carts, is a common task that characterizes any manufacturing or service operation, and there is always a significant human input to those operations in terms of physical load. The physical load represents the effect of input forces during MMH operations that depend on the interaction between material handling equipment and the working environment. Many times MMH represents a critical issue related to human-machine interaction due to the carts can work in environment with parameters different from those used in designing, subjecting workers to risk of musculoskeletal disorders. The aim of this work, developed in collaboration with Fiat Chrysler Automobiles (FCA), is to develop a new procedure that allows estimating the initial and the maintenance forces necessary to push or pull carts, knowing the characteristics of the cart and the environment in which it works, in order to preventively assess the ergonomic indexes according to ISO 11228-2. The procedure is based on multibody simulations. The cart is modeled by Computer Aided Design (CAD) code and, then, imported in a multibody code where numerical simulations are performed in order to calculate the forces. In the multibody code static and dynamic friction coefficients of bearing of wheels are assigned, together with parameters of contact between wheels and floor. Changing the pivot angle of two floating wheels, several simulations have been carried out. Moreover, considering a cart used at the assembly line of the FCA plant of Pomigliano d'Arco (Naples), experimental tests have been performed in order to validate the procedure by comparing numerical results with the experimental ones.

Keywords: Ergonomics , Material Manual Handling , Multibody , Pushing/Pulling actions

In this paper, a new methodology supporting the design of landing gears is proposed. Generally, a preliminary step is performed with simplified FE model, usually one-dimensional, to achieve the reaction forces involving each component during all aforementioned aircraft operations. Though this approach gives a valid support to the designer, it is characterized by several problems, such as the related approximations. So, it is important, by a numerical point of view, to develop an isostatic FE model equivalent to the real one. In fact, if the landing gear is modelled as hyperstatic, the static equilibrium equations are insufficient for determining the internal forces and reactions on each sub-component; so, the modelled material properties and geometries assume an increasing importance, which gets the model too approximating. The proposed methodology consists of achieving the reaction forces by means of multibody simulations, by overcoming such problems, since each component is modelled as rigid. In this paper, also a FE model for the investigation of the structural response is proposed. Aimed to Certification by Analysis purposes, the developed multibody and the FE models have been assessed against an experimental landing gear drop test carried out by Magnaghi Aeronautica S.p.A., according to the EASA CS 25 regulations.

Keywords: Drop test , Dynamic behaviour , FE analysis , Landing gear , Multibody

In nearly every sector of industrial manufacturing, especially the mould and die making industry, polishing techniques are used. Most often, manual polishing is the only option because the tasks are too complex to be automated in terms of surface quality demands, geometrical features and restricted tool accessibility. Therefore, the European H2020 Project SYMPLEXITY 'Symbiotic Human-Robot Solutions for Complex Surface Finishing Operations' developed a CNC-machine-based machining concept comprising a composition of different finishing technologies. The solution is complemented with an objective metrology surface qualification device, which is capable to also measure big parts holistically. The SYMPLEXITY approach combines both a collaborative, intelligence-based and a cooperative human-robot-based technological approach. The demonstrator machine concept is being introduced and first fine machining experiments, comprising polishing and measurements have been conducted to generate an initial parameter set-up. The experiments have been conducted on an empiric basis to identify the main steering parameters for a future semi-analytic, model-based finishing approach.

Keywords: Abrasive Finishing , Human-Robot Interaction , Objective Surface Qualification , Robotic polishing

This study proposes a novel automatic method for facial landmark localization relying on geometrical properties of 3D facial surface working both on complete faces displaying different emotions and in presence of occlusions. In particular, 12 descriptors coming from Differential Geometry including the coefficients of the fundamental forms, Gaussian, mean, principal curvatures, shape index and curvedness are extracted as facial features and their local geometric properties are exploited to localize 13 soft-tissue landmarks from eye and nose areas. The method is deterministic and is backboned by a thresholding technique designed by studying the behaviour of each geometrical descriptor in correspondence to the locus of each landmark. Occlusions are managed by a detection algorithm based on geometrical properties which allows to proceed with the landmark localization avoiding the covered areas. Experimentations were carried out on 3132 faces of the Bosphorus database and of a 230-sized internal database, including expressive and occluded ones (mouth, eye, and eyeglasses occlusions), obtaining 4.75 mm mean localization error.

Keywords: 3D face , Differential geometry , Face analysis , Feature extraction , Landmark localization

Purpose: The aim of this in vitro study was to verify whether or not stock and computer-aided design/ computer-aided manufacturing (CAD/CAM) abutments show similar precision in the connection with the respective implants. Materials and Methods: Ten CAD/CAM titanium abutments were compared with 10 stock titanium abutments. Each abutment fit a regular-platform implant (Institute Straumann). Implants and abutments were measured independently and then connected. During the connection procedure, the torque was measured using a six-axes load cell. Then, outer geometric features of the implant-abutment connection were measured again. Finally, the assembly was sectioned to provide the analysis of inner surfaces in contact. The geometric measurements were performed using a multisensored opto-mechanical coordinate measuring machine. The following parameters were measured and compared for the CAD/CAM and stock titanium abutment groups, respectively: width of interference and interference length between the conical surfaces of the implant and abutment; and volume of material involved in the implant-abutment connection. Results: Interference width mean ± SD values of 18 ± 0.5 and 14 ± 0.5 μm were calculated for the stock and CAD/CAM titanium abutment groups, respectively. The difference was statistically significant (P = .02). Furthermore, the interference length mean ± SD values of 763 ± 10 and 816 ± 43 μm were calculated for stock and CAD/CAM titanium abutment groups, respectively. The difference was also statistically significant (P = .04). Finally, the volume of material involved in the implant-abutment connection was compared between stock and CAD/CAM titanium abutment groups; the mean ± SD values of 0.134 ± 0.014 and 0.108 ± 0.023 mm3 were significantly different (P = .009). Conclusion: Both standard and CAD/CAM abutment groups showed a three-dimensional (3D) seal activation after the screw tightening. Nevertheless, stock titanium abutments showed a significantly higher volume of material involved in the implant-abutment connection compared with that of CAD/CAM titanium abutments.

Keywords: CAD/CAM abutments , Implant-abutment connection , Stock titanium abutments

In the present work a novel rear suspension for motorcycles, able to achieve the required progressiveness in terms of rigidity by using a constant-stiffness spring and an innovative compact mechanism, is studied. The key component is an eccentric system inserted in the shock absorber head. As reference, the rear suspension of the Ducati Multistrada MY 2010, characterized by the use of a variable-stiffness spring, is analyzed. The aim of the paper is to prove that the novel proposed solution can obtain a response, in terms of wheel load, similar to that of the reference system. At first, a mathematical model to simulate the kinematics of the novel suspension is presented. This model is able to evaluate the influence of geometric dimensions of the components, checking successfully the ability to reproduce the behavior of the original suspension. After the preliminary design, the kinetostatic model is included within an optimization algorithm ad-hoc created to obtain the optimum dimensions of each component. In order to obtain the inertial parameters, two 3D models of both the suspensions are created. Finally, two multibody models of the two suspensions are implemented in Adams environment in order to evaluate their dynamic behaviour. Results confirm the goodness of the novel solution being comparable to the reference one in terms of dynamic response during the simulation of a typical experimental test performed in Ducati.

Keywords: Constant stiffness spring , Eccentric mechanism , Integrated simulation , Motorcycle rear suspension , Multibody dynamics

Collaborative robots must operate safely and efficiently in ever-changing unstructured environments, grasping and manipulating many different objects. Artificial vision has proved to be collaborative robots' ideal sensing technology and it is widely used for identifying the objects to manipulate and for detecting their optimal grasping. One of the main drawbacks of state of the art robotic vision systems is the long training needed for teaching the identification and optimal grasps of each object, which leads to a strong reduction of the robot productivity and overall operating flexibility. To overcome such limit, we propose an engineering method, based on deep learning techniques, for the detection of the robotic grasps of unknown objects in an unstructured environment, which should enable collaborative robots to autonomously generate grasping strategies without the need of training and programming. A novel loss function for the training of the grasp prediction network has been developed and proved to work well also with low resolution 2-D images, then allowing the use of a single, smaller and low cost camera, that can be better integrated in robotic end-effectors. Despite the availability of less information (resolution and depth) a 75% of accuracy has been achieved on the Cornell data set and it is shown that our implementation of the loss function does not suffer of the common problems reported in literature. The system has been implemented using the ROS framework and tested on a Baxter collaborative robot.

Keywords: Collaborative robotics , Deep learning , Engineering methods , Vision-guided robotic grasping

In several application contexts, virtual solid models require to integrate portions of polygonal meshes with synthetic models, designed by traditional parametric/analytical multipatches systems. The paper reports the research aiming at covering the theoretical and numerical aspects connected with an extended geometric solid modeling system, focusing on the B-Rep models and introducing the new paradigm of Extended B-Rep (EB-Rep), which is able to integrate mesh-faces as part of a B-rep model. This paradigm introduces a notion of continuity between parametric and discrete representations, regularized Boolean Operations, a join operator and an approach to represent a valence semi-regular mesh as an EB-Rep structure. A prototype of the geometric solid modeling kernel has been realized and tested in the OpenCascade library environment.

Keywords: B-Rep , polygonal meshes , regularized boolean operations , Solid modeling kernel

3D recording, digital surveying and mapping are efficient and manageable tools for reconnaissance, documentation and monitoring in underwater archaeology. Lab4Dive project, co-funded by the European Union's EMFF Programme, through the EASME and DG MARE call on 'Blue Labs', aims to design, develop and validate an innovative, marketable and competitive technology, which will assist underwater archaeologists in the field and will contribute significantly to the successful outcome of the survey process, documentation and preservation of submerged archaeological sites. In this article, the Lab4Dive system and its preliminary testing results, will be presented. The system is based on an underwater tablet coupled with an intelligent underwater case embedded with environmental sensors, a high-resolution camera and compatible with different commercial acoustic positioning systems, which will be integrated with a cloud data gathering system. During the dive, the tablet provides the diver with an augmented navigation interface, which guides him towards the selected targets. The cloud data gathering system allows the archaeologists to produce a 3D reconstruction of the site, which encompasses all the acquired information, enabling them to further study and analyze the data before the next mission.

Keywords: 3D documentation , 3D Reconstruction , IoT , Marine Robotics , Underwater Archaeology