Geometric modeling and processing

In the field of additive manufacturing (AM) processes, there is a significant lack of scientific data on the performance of open-source 3D printers in relation to process parameter values. The purpose of this paper is to assess the impact of the main process parameters on the accuracy of a set of typical geometric features, as obtained with an open-source 3D printer, the RepRap Prusa-Mendel I2. For this purpose, a benchmarking part was set up, composed of elementary shapes, representing a series of different geometric features. By means of a DoE approach, it was possible to assess the effects of two process parameters - layer thickness (Lt) and flow rate (Fr) - on five geometric features: cube, sphere, cylinder, cone, and angled surface. A high resolution Laser Scanner was used to evaluate the variation between the acquired geometric feature and the corresponding 3D computer-aided design (CAD) nominal model. On the basis of experimental results, it was possible to analyze and discuss the main effects of the above-mentioned process parameters on each geometric feature. These results can help RepRap users in the correct selection of process parameters with the aim of improving the quality of prototypes.

Keywords: geometric features , laser scanner , open-source 3D Printers , process parameters

Purpose - This study aims to quantify the ultimate tensile strength and the nominal strain at break (f) of printed parts made from polylactic acid (PLA) with a Replicating Rapid prototyper (Rep-Rap) 3D printer, by varying three important process parameters: layer thickness, infill orientation and the number of shell perimeters. Little information is currently available about mechanical properties of parts printed using open-source, low-cost 3D printers. Design/methodology/approach - A computer-aided design model of a tensile test specimen was created, conforming to the ASTM:D638. Experiments were designed, based on a central composite design. A set of 60 specimens, obtained from combinations of selected paramers, was printed on a Rep-Rap Prusa I3 in PLA. Testing was performed using a JJ Instruments - T5002-type tensile testing machine and the load was measured using a load cell of 1,100 N. Findings - This study investigated the main impact of each process parameter on mechanical properties and the effects of interactions. The use of a response surface methodology allowed the proposition of an empirical model which connects process parameters and mechanical properties. Even though results showed a high variability, additional ideas on how to understand the impact of process parameters are suggested in this paper. Originality/value - On the basis of experimental results, it is possible to obtain practical suggestions to set common process parameters in relation to mechanical properties. Experiments discussed in the present paper provide a variety of data and insight regarding the relationship among the main process parameters and the stiffness and strength of fused deposition modeling-printed parts made from PLA. In particular, this paper underlines the shortage in existing literature concerning the impact of process parameters on the elastic modulus and the strain to failure for the PLA. The experimental data produced show a good degree of compliance with analytical formulations and other data found in literature.

Keywords: Central composite design , Nominal strain at break , Open-source 3D printers , Polylactic acid , Process improvement , Ultimate tensile strength

The geometric segmentation of a discrete geometric model obtained by the scanning of real objects is affected by various problems that make the segmentation difficult to perform without uncertainties. Certain factors, such as point location noise (coming from the acquisition process) and the coarse representation of continuous surfaces due to triangular approximations, introduce ambiguity into the recognition process of the geometric shape. To overcome these problems, a new method for geometric point identification and surface segmentation is proposed. The point classification is based on a fuzzy parameterization using three shape indexes: the smoothness indicator, shape index and flatness index. A total of 11 fuzzy domain intervals have been identified and comprise sharp edges, defective zones and 10 different types of regular points. For each point of the discrete surface, the related membership functions are dynamically evaluated to be adapted to consider, point by point, those properties of the geometric model that affects uncertainty in point type attribution. The methodology has been verified in many test cases designed to represent critical conditions for any method in geometric recognition and has been compared with one of the most robust methods described in the related literature.

Keywords: Discrete differential geometry , Discrete surfaces , Geometric segmentation

The present paper proposes a new method for axis identification in discrete axially symmetrical geometric models. This method is based on-a-never-used-before property of the axially symmetrical surfaces for which the symmetry line of any section curve of the surface (or of a portion of it in the case of an incomplete axially symmetrical surface) always intersects the axis of symmetry of the surface. Thus the working principle of the method makes it very robust to local defectiveness, measurement noise and outliers. In order to compare it with the most cited methods presented in literature, several types of tests have been designed and performed. The robustness of those methods, on the one hand, has been evaluated by defining the Statistical Confidence Boundary at 1σ confidence level. The trueness of the method, on the other hand, has been evaluated on geometric models obtained by measuring real objects. The high robustness, which characterizes the proposed method, makes it particularly suitable for product geometric inspection where high accuracy is required.

Keywords: Axis identification , Geometric inspection

The paper deals with the relationship between geometrical or topological entities of complex systems and the physics in which the systems are involved. In particular, the paper deepens the integration of thermal physics with geometrical constraints. Therefore, the results of the work could be used within the development of a 3D-multiphysical sketcher viz., a tool for the preliminary design of complex systems, characterized by the presence of one or more overlapping physics. Firstly, the model of Topologically & Technologically Related Surfaces (TTRS) is used and related Minimal Reference Geometrical Elements (MRGEs) and constraint conditions are implemented by means of Modelica language. Then, the implementation of new objects for MRGEs and constraint conditions are applied to a mechanical assembly. Finally, the integration of TTRS model within thermal physics is applied to the case of the layout designing for electronic boards.

Keywords: Modelica language , Multiphysics , preliminary design , TTRS

The main objective of this work was to design an innovative skidding winch aimed to improve timber harvesting productivity, operators' safety, and reduce environmental damage in contexts in which mechanized harvesting is limited. The study area is the north-western Black Sea region of Turkey. In the proposed methodology, the harvesting process was simulated with Discrete Event Simulation (DES) software in order to identify bottlenecks. An alternative process was compared with the original one within the DES software itself in order to validate further steps oriented to generate new innovative product concepts. The development of the product was focused towards customer satisfaction, collecting customer requirements and identifying quality characteristics with a Quality Function Deployment approach. Contradictions identified in the design phase were solved using the TRIZ contradiction toolkit, generating different product concepts. Inventive solutions provided by TRIZ were designed within parametric CAD software. The concepts were compared in virtual environment with focus on ergonomics, selecting an optimal solution. The results show that with the concept adopted is possible to achieve a substantial increase in productivity, from 121% to 133%, in terms of kilograms of logs per hour deposited on the landing. Moreover, the final concept allows for ergonomic loading operations and reduces environmental damage to soil and vegetation.

Custom-fit products, such as artificial prostheses, often require the development of hoc modeling tools and procedures. In such a context, this paper describes an open source library, named Simply NURBS, developed for NURBS modeling in medical and health-care domains. This new suite makes available a development kit that integrates the key features of existing open source libraries and new ones to fulfill the requirements of the considered domain. First, the paper introduces the library requirements with particular attention to the prosthetic field as well as pros and cons of current NURBS modeling libraries (both commercial and open sources). Then, the software architecture of Simply NURBS and the basic libraries (e.g., OPENCASCADE and NURBS++) used for its implementation are illustrated enhancing differences and improvements. Finally, a socket modeling tool, named Virtual Socket Laboratory (VSL) developed using SimplyNURBS is described as well as results of tests carried out to evaluate the new system performances.

Keywords: Nurbs , Open source libraries , Prosthetic socket

The research work presented in this paper is part of an innovative framework that deals with the design process of lower limb prostheses. The quality of the whole prosthesis depends on the comfort of the socket, which realizes the interface between the patient body and the mechanical parts. We developed a CAD system, named Socket Modelling Assistant that guides the user during the design of the socket, exploiting domain knowledge and design rules. In this work we present a preliminary study that describes the implementation of a software module able to automatically identify the critical areas of the residuum to adequately modify the socket model and reach the optimal shape. Once the critical areas have been identified, the Socket Modelling Assistant can apply proper geometry modifications, in order to create the load and off-load zones for a good pressure distribution over the residual limb.

Keywords: CAD , Lower limb prosthesis , Neural network , Prostheses socket

The paper concerns the use of integrated methodologies and tools to perform innovative human centered development of products. Digital simulation of ergonomics by means of DHM is shown together with advanced tools for design, taking into account Knowledge-based systems, Design Automation and design of highly customized goods. Two different applications of the proposed approach are described, the first refers to an industrial product, the second to the medical domain. Both applications, even if belonging to completely different fields benefit from putting the human at the center of the developing paradigm from the very first step of product development. Some results and discussion highlight benefits and limitation of the approach and of the adopted tools.

Keywords: Design Automation , Digital human modelling , Ergonomics , Human centered design , Knowledge-based systems , Lower limb prosthesis

Remote Laser Welding (RLW) is a joining technique more recent than the most known and widely adopted (mainly in the automotive field) resistance spot welding technique (RSW). While RLW offers much more benefits than RSW (higherprocess speed, less number of operating robots, decreased factory floor footprint, reduced overall process costs), it also adds issues related to process planning and quality control of welded joints. The European Commission, under the ICT-Factories of the Future programme of FP7, funded a project, starting from January 2012 and just ended on June 2015, titled "RLW Navigator - Remote Laser Welding System Navigator for Eco Resilient Automotive Factories" which aims at developing an innovative Process Navigator for planning, integrating, testing and validating applications on the use of RLW in the automotive assembly addressing today's critical needs for frequently changing operating conditions and product-mix provisions. The project results are a set of toolboxes able to offer very useful tools to plan and control the RLW joining process. The key word that mainly describes the provided ICT-based solutions is Optimisation: from the optimisation of the working cell, by analysing several layout configurations, to the optimisation of robot path and weld sequencing for assigned product and process constraints; from the fixture optimisation (involving the best clamp configuration) starting from real/non-ideal shape parts, to the optimisation of process laser parameters to guarantee higher welded join quality. The applicability of these software tools goes beyond the automotive field and this makes the provided solutions much more interesting for the industry.

In the present work the structural behaviour of a mandible with a dental implant, considering a unilateral occlusion, is numerically analysed by means of the Finite Element Method (FEM) and the Boundary Element Method (BEM). The mandible, whose CAD model was obtained by computer tomography scans, is considered as completely edentulous and only modelled in the zone surrounding the implant. The material behaviour of bone is assumed as isotropic linear elastic or, alternatively, as orthotropic linear elastic. With reference to the degree of osteo-integration between the implant and the mandibular bone, a partial osteo-integration is considered; consequently a nonlinear contact analysis is performed, with allowance for friction at the interface between implant and bone. A model of a commercial dental implant is digitised by means of optical 3D scanning process and fully reconstructed in all its geometrical features. Special attention is drawn to the mathematical reconstruction of the CAD model in order to facilitate the meshing process in the BEM environment and reduce the geometrical imperfections generated during the CAD to CAE translation process. The results of FEM and BEM analyses in terms of stress distribution on the mandible are compared in order to benchmark the two methodologies against accuracy and pre-processing efforts.

Keywords: BE modelling , Dental implant , FE modelling , Non-linear contact analysis

One of most demanding tasks in the manufacturing field is controlling the variability of parts as it may affect strongly the deliverability of key characteristics defined at the final (product) assembly level. Current CAT systems offer a good solution to the tolerance analysis/synthesis task, but to handle flexible objects with shape errors more effort is needed to include methods able to capture the elastic behaviour of parts that adds more variability on the final assembly. Usually, sheet metal assemblies require dedicated fixtures and clamps layout to control the gap between parts in the specific location where a join must be placed. Due to the variability of parts the position of clamps can also be varied. The paper describes a FEM-based method able take into account part flexibility and shape error to parametrically analyse sheet metal assemblies by acting on some key parameters to look for the optimal clamp layout that guarantee the gap between parts to be under control after joining parts together. This method offers, with respect to commercial solutions, the ability to model fixtures, clamps and different joint types with no matter on the node positions of the mesh. Locations of such elements are based on the shape functions defined at element (shell) mesh level and modelled as local constraints. So the user can generate a mesh without a previous knowledge of the exact positions of clamps, for example. This allows to conduit a parametric analysis without remeshing the surfaces and with no need to physically model the clamps. An aeronautic case study is described with a four-part assembly riveted on a quite complex fixture by using several clamps.

Keywords: Clamp layout optimisation , Compliant assemblies , Free shape variability , Sheet metal parts , Shell.

This paper explores a possible integration of some ancillary systems of helium-cooled lithium lead (HCLL) and helium-cooled pebble-bed (HCPB) test blanket modules in ITER CVCS area. Computer-aided design and ergonomics simulation tools have been fundamental not only to define suitable routes for pipes, but also to quickly check for maintainability of equipment and in-line components. In particular, accessibility of equipment and systems has been investigated from the very first stages of the design using digital human models. In some cases, the digital simulations have resulted in changes in the initial space reservations.

Keywords: CAD , Design for maintainability , Digital human modeling , Piping layout design

In the field of orthodontic planning, the creation of a complete digital dental model to simulate and predict treatments is of utmost importance. Nowadays, orthodontists use panoramic radiographs (PAN) and dental crown representations obtained by optical scanning. However, these data do not contain any 3D information regarding tooth root geometries. A reliable orthodontic treatment should instead take into account entire geometrical models of dental shapes in order to better predict tooth movements.This paper presents a methodology to create complete 3D patient dental anatomies by combining digital mouth models and panoramic radiographs. The modeling process is based on using crown surfaces, reconstructed by optical scanning, and root geometries, obtained by adapting anatomical CAD templates over patient specific information extracted from radiographic data. The radiographic process is virtually replicated on crown digital geometries through the Discrete Radon Transform (DRT). The resulting virtual PAN image is used to integrate the actual radiographic data and the digital mouth model. This procedure provides the root references on the 3D digital crown models, which guide a shape adjustment of the dental CAD templates. The entire geometrical models are finally created by merging dental crowns, captured by optical scanning, and root geometries, obtained from the CAD templates.

Within the orthodontic field, malocclusion problems are usually treated by using different types of appliances. In particular, Eruption Guidance Appliances (EGAs) are recommended for early orthodontic treatment or prevention of malocclusion problems. The traditional approach with EGAs is based on the use of standard prefabricated appliances. Experts in the orthodontic field believe that the customization of the EGAs would strongly enhance the results of malocclusion treatments. This paper presents an innovative methodology for the design and manufacturing of fully customized EGAs. The methodology is based on an extensive integration between traditional orthodontic procedures with advanced computer aided design processes. The methodology moves from the digitalization of the plaster models obtained by optical scanning techniques. The patient morphology is then exploited, under dental practitioner supervision, for the design of the appliance geometry through CAD modeling tools. Medical guided assessment is required throughout the most of the data elaboration processes, in order to design the EGAs accordingly to the patient's clinical conditions. Low-pressure injection molds for the physical manufacturing of the appliances are then 3D printed by using rapid prototyping techniques. The proposed methodology allows the production of patient customized appliances guaranteeing low cost manufacturing and high quality standards, similar to those typically obtained by in series productions. Moreover, the presented approach offers a high integration level with numerical and finite element methods, which can be used for evaluating the stress applied on the EGA, thus allowing the reinforcement of the appliance prior its manufacturing.

The EU Directive 49/2002/EC on Environmental Noise refers to Quiet Urban Areas (QUAs) as places whose acoustic climate should be preserved because a noise indicator is lower than a threshold established by each Member State. This definition appears to be extremely generic and doesn't provide usable procedures to be applied in each Country. Proposing a solution to overcome the lack of harmonized methodologies for QUAs is the main aim of QUADMAP (QUiet Areas Definition and Management in Action Plans) Project. The results of the Project will facilitate urban planners to apply standard procedures for identification, delimitation and prioritization of QUAs. The Project has a high level of demonstrativeness guaranteed by the fact that the proposed methodology has been tested in a number of pilot areas in Florence (Italy), Bilbao (Spain) and Rotterdam (The Netherlands). The Project started on 1st September 2011 and lasts three years and half. At the beginning of 2013 the harmonized methodology has been defined. The proposed procedures have been tested since February 2013 in all pilot cases and the methodology has been improved, in line with experiences gained during data collection and analysis of the ante-operam scenarios. Since the beginning of 2014, the realization of interventions started, following indications coming from endusers questionnaires, expert analysis, technicians and application of complementary criteria. In the pilot areas of Bilbao interventions have been completed by June 2014, while in Florence and Rotterdam they have been concluded by the end of the same year. In the meantime, post-operam data collection and analysis have started. In this paper results of the post operam data analysis are described and compared with those obtained on the ante-operam phase. Moreover, the main innovative elements introduced in the optimized methodology are illustrated.

In accordance to the recommendations of the 2001 UNESCO Convention on the Protection of Underwater Culturage Heritage in the last years many projects have been founded and are now underway developing and testing new techniques and tools to support in-situ conservation of underwater archaeological remains. This paper describes the contribution of the CoMAS project ('In situ conservation planning of Underwater Archaeological Artefacts' - www.comasproject.eu) in the development of innovative electromechanical devices that can efficiently support the cleaning process of submerged archaeological structures.

Keywords: electromechanical devices , restoration , underwater archaeological artefacts

This paper presents an immersive virtual reality system that includes a natural interaction approach based on free hand gestures that is used to drive a Desktop Haptic Strip for Shape Rendering (DHSSR). The DHSSR is a mechatronic display of virtual curves intersecting 3D virtual objects, and aims at allowing designers to evaluate the quality of shapes during the conceptual design phase of new products. The DHSSR consists of a 6DOF servo-Actuated developable metallic strip, which reproduces cross-sectional curves of 3D virtual objects. Virtual curves can be interactively generated on the 3D surface of the virtual object, and coherently the DHSSR haptic interface renders them. An intuitive and natural modality for interacting with the 3D virtual objects and 3D curves is offered to users, who are mainly industrial designers. This consists of an immersive virtual reality system for the visualization of the 3D virtual models and a hand gestural interaction approach used by the user for handling the models. The system has been implemented by using low cost and open technologies, and combines a software engine for interactive 3D content generation (Unity 3D), the Oculus Rift Head Mounted Display for 3D stereo visualization, a motion capture sensor (LeapMotion) for tracking the user's hands, and the Arduino Leonardo board for controlling the components. Results reported in the paper are positive for what concerns the quality of the rendering of the surface, and of the interaction modality proposed.

This paper presents a hand gestural interaction system that is used to handle a Desktop Haptic Strip for Shape Rendering (DHSSR). The strip is a physical display of virtual curves intersecting 3D virtual objects, and aims at allowing designers to evaluate the quality of shapes during the conceptual design phase of new products. The DHSSR consists of a servo-actuated developable metallic strip, which reproduces cross-sectional curves of 3D virtual objects. In order to generate the virtual curve intersecting the virtual object it has been implemented a hand gestural interaction system, which allows moving the curve or the 3D object. Specifically, through an interaction approach based on a magnetic pinch the user can move the virtual strip until reaching the desired position. Instead, an interaction modality based on index finger recognition allows moving the 3D object while the virtual curve is floating in space. The virtual curve generated by the interaction is used for deforming the physical strip. The hand gestural interaction system has been implemented by using low cost and open technologies, and combines an engine for interactive 3D content generation (Unity 3D), a motion capture sensor (LeapMotion) and the Arduino Leonardo board. In particular, the user's hands are tracked by means of the Leap Motion sensor. The Unity 3D environment is used to virtually render the virtual objects (curve and shape) and the virtual avatar of the users' hands. The virtual environment is connected with the Arduino Leonardo board in order to control the six servo-actuators of the DHSSR. The paper also presents some studies performed to evaluate the performances of the DHSSR system and the usability of the hand gestural interaction modalities.

Keywords: Hand gestural interaction , Haptic strip , Motion capture sensor , Shape rendering

This paper presents a new concept of a desktop tangible shape display for virtual surface rendering. The proposed system is able to represent in the real environment the shape of a digital model of a product, which can be explored naturally through a free-hand interaction. Aim of the shape display is to allow product designers to explore the rendered surface through a continuous touch of curves lying on the product shape. Ideally, the designer selects curves, which can be considered as style features of the shape, on the shape surface, and evaluates the aesthetic quality of these curves by manual exploration. In order to physically represent these selected curves, a flexible surface is modelled by means of servo-actuated modules controlling a physical deforming strip. The behaviour of the strip is controlled by acting on the position and rotations of a discrete number of control sectors. Each control sector is controlled by a module, which is based on an absolute positioning approach and equipped with five degrees of freedom. The developed system is able to manage the elastic behaviour of the strip in terms of bending, twisting and local tangency. The tangency control allows us to manage the local tangency of the strip to the rendered trajectory, thus increasing the accuracy of the representation. Moreover, a preliminary second version of the module is presented, which has been designed so as to allow the control sectors to slide on the strip. Thanks to this feature, it will be possible to place the control sector in a given point of the trajectory, such as point of maximum, point of minimum or inflection points. The device is designed to be portable, low cost, modular and high performing in terms of types of shapes that can be represented. A prototype equipped with three modules has been developed in order to evaluate the usability and the performances of the display.