Geometric modeling and processing

The participation of blind people (BP) in cultural life can be improved by enhancing methodologies and tools for facilitating the 3D reproduction of artworks and, at the same time, to facilitate their exploration. The creation of integrated systems including not only tactile media such as, for instance, sculptures or bas-reliefs but even a set of tools capable of providing the users with an experience cognitively comparable to the one originally envisioned by the artist, may undoubtedly enhance artworks exploration. The present work aims to design a conceptual system to aid BP in the tactile exploration of bas-reliefs. This conceptual system comprises both a hand-tracking system and an audio device, together with a number of methodologies, algorithms and information related to physical design. The designed layout, preliminarily tested to understand its potential and limits, proved to be a promising first attempt in enhancing the BP exploration experience.

Keywords: 3D reconstruction , Blind people , Hand-tracking system , Tactile bas-relief , Tactile exploration

This paper describes the features of AMCOMP, a CAD environment conceived to manage the computation of the Added Masses of bodies moving in an infinite fluid. A methodology already published in literature has been implemented in a CAD environment and its features are exploited to perform the evaluation of the Added Masses. These include the importing of the model in STL file format and the computation of the complete Added Mass matrix and non-dimensional terms. The CAD has been validated by computing the Added Masses values of bodies whose exact formulation was found in literature. The validated tool has been applied to more complex case studies where the Added Masses values were guessed using empirical laws or the equivalent ellipsoid approximation. Significant differences have been found between approximated methods and computations on real shapes. It is shown that the precision in the Added Masses computation and the computational time depend on the meshing quality of the model and power of the PC on which the software runs. Several tools have been merged to obtain a model useful for the Added Masses computation and to assess the errors arising from using approximated formulas instead of the real shape of the body.

Keywords: Added Masses , Computer Aided Design , Conceptual design , User interface

The mounting attention to environmental issues requires adopting better disassembly procedures at the product's End of Life. Planning and reckoning different disassembly strategies in the early stage of the design process can improve the development of sustainable products with an easy dismissing and recycling oriented approach. Nowadays many Computer Aided Process Planning software packages provide optimized assembly or disassembly sequences, but they are mainly based on a time and cost compression approach, neglecting the human factor. The environment we developed is based upon the integration of a CAD, an Augmented Reality tool, a Leap Motion Controller device, see-through glasses and an algorithm for disassembly strategies evaluation: this approach guarantees a more effective interaction with the 3D real and virtual assembly than an approach relying only on a CAD based disassembly sequence planning. In such a way, the operator may not test in a more natural and intuitive way automatic disassembly sequences, but he/she can also propose different strategies to improve the ergonomics. The methodology has been tested in a real case study to evaluate the strength points and criticalities of this approach.

Keywords: Augmented Reality , CAD , Design for Disassembly , Disassembly Sequence Optimization

This paper presents the development of a CAD conceived to support the modelling of lightweight and lattice structures just from the initial stages of the design process. A new environment, called LWSM (acronym of LightWeight Structures Modelling), has been implemented in Python programming language in an open-source CAD software to allow the fast modelling of several sandwich structures or the filling of solid parts with cubic and tetrahedral lattice structures which can be produced by Additive Manufacturing (AM) techniques. Several tests have been carried out to validate the tool, one of which is included in the paper. The design of a bracket component inside LWSM using a traditional dense geometry and a lattice structure is described. The use of Design for Additive Manufacturing (DfAM) functions helps the user in the design of innovative structures which can produced only with AM technologies. A significant change in the shape of the part respect to traditional solutions is noticed after the use of DfAM functions by experimenters: FEM analysis confirms a strong weight reduction.

Keywords: Additive manufacturing , CAD , FEM analysis , Lattice structure , Lightweight structures

PMI annotations are widely used to support the Model Based Design within modern companies. In particular, the introduction of digital annotations marks the transition from the 2D drawings to the 3D representation in many manufacturing and design companies. However, today the implementation of the PMI technology presents some limits, such as the lack of functions to generate structure templates to be applied to similar CAD models. The proposed approach aims to overcome the limits of traditional tools which are not able to add a PMI annotation's structure from one model to another one. The paper describes a method to reuse digital PMI annotations in a new model during the design phase, where the annotations are inherited from similar CAD documents. The proposed approach is based on two levels of geometric analysis: the searching of similar template models from an XML database, and the identification of the related geometric entities, which are used as associated objects for the definition of 3D annotations. The test case is focused on the automatic generation of PMI annotations for exhaust duct items used in oil & gas applications. The proposed tool has been developed within a software program called Duct Designer, which is used for the CAD automation of duct items. Particularly, the test case enhances the retrieval and reuse of sizing schemes from previous 3D models in order to obtain an automatic rebuilding of the geometric annotations.

Keywords: Digital annotations , Model-based definition (MBD) , Oil & gas , Product manufacturing information (PMI)

In the fabrication process of aspheric glass lens and molds, shape characterization is a fundamental task to control geometrical errors. Nevertheless, the more significant geometrical functional aspect related to the optical properties is the curvature, which is rarely investigated in the manufacturing process of lenses. Algorithms for the assessment of shape and curvature errors on aspheric surface profile are presented. The method has been investigated on profiles measured before and at different steps of the membrane polishing process. The results show how surface roughness, shape, and curvature change during the polishing process as a function of the machining time.

Keywords: Curvature , Glass , Grinding , Polishing , Roughness , Shape

Sintering shrinkage of uniaxially cold compacted axi-symmetrical parts is anisotropic. Not only is the shrinkage of height (parallel to the compaction direction) different from that of the diameters (in the compaction plane), but even the dimensional changes of the inner and of the outer diameters differ significantly. This behaviour has been investigated on iron rings with different geometry and green density. In the compaction plane radial and tangential shrinkages are different, and tangential shrinkage significantly changes along the wall thickness. This is due to the distribution of radial and tangential stresses during cold compaction that in turn depends on the axial stress. The stress field and its dependence on both green density and geometry were hypothesized to propose a working direction to interpret the anisotropy of sintering shrinkage in real parts.

Keywords: Geometry , Green density , Sintering shrinkage

The Strait of Messina is a very busy sea area that separates Sicily and the Italian mainland. In respect of environment and for the prevention of human loss, it is fundamental to have an estimate of the possible ship accidents that could occur. In this work, the approach used is the International Association of Lighthouse Authorities Waterways Risk Assessment Program (IWRAP) model. The first part of the paper describes the local and global traffic and the separation scheme in the Strait of Messina. The model input data is obtained from the Vessel Traffic Service (VTS) system thanks to the Coast Guard of Messina. The second part concerns calculation of the geometrical collisions (number of collisions in different scenarios) and the causation probability. This analysis is the basis for the discussion of new regulatory constraints due to the future realisation of new piers in the south and the planned unification of the two Port Authorities of the two shores into one single authority.

Keywords: Marine traffic safety , Regulatory and environmental constraints , Safety design , Ship collision

A feasibility study was performed in order to demonstrate the benefits of designing and manufacturing a customized foot orthosis by means of digital technologies, such as Reverse Engineering (RE), Generative Design (GD) and Additive Manufacturing (AM). The aim of this work was to define the complete design-manufacturing process, starting from the 3D scanning of the human foot anatomy to the direct fabricating of the customized foot orthosis. Moreover, this first methodological study tries to combine a user-friendly semi-automatic modelling approach with the use of low-cost devices for the 3D laser scanning and the 3D printing processes. Finally, the result of this approach, based on digital technologies, was also compared with that achieved by means of conventional manual techniques.

Keywords: Additive manufacturing , Computer aided design , Foot orthosis , Generative design , Reverse engineering

The paper presents a description of a methodology to accurately estimate the natural frequencies of a hybrid metal-composite gear, where the web is made of a polymer matrix reinforced with two-dimensional (2D) triaxial braided fabrics. The proposed approach is based on a multi-scale composite modeling starting from evaluation of homogenized material properties of the gear web at the meso-scale for a subsequent FE-based modal analysis. For this purpose, the mechanical behavior of a single Repetitive Unit Cell (RUC) at the meso-scale is analyzed with a FE procedure which takes into account the interweaving and cross-section geometry of the yarns, volume fraction and local fiber orientation. It is shown that the described modeling strategy allows to predict gear's natural frequencies that are close to the experimental results. Significant accuracy enhancement is achieved with respect to the model in which the web material is considered as perfectly isotropic.

Keywords: Hybrid gears , Mechanical transmissions , Modal analysis , Multi-scale modeling , Triaxial braided fabrics

Titanium and its alloys are widely used in cranioplasty because they are biocompatible with excellent mechanical properties and favor the osseointegration with the bone. However, when Titanium alloys have to be worked several problems occurred from a manufacturing point of view: the standard procedure for obtaining Titanium prostheses is represented by the machining processes, which result time and cost consuming. The aim of this research consist to introduce alternative 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 research activities have already highlighted the potentiality of the investigated forming processes that can be alternatively used taking into account both the damage morphology and the need of urgency operation. In the present work, the way of manufacturing the Ti prostheses by SPF and SPIF is described. A comparative analysis has been performed, thus highlighting the peculiarities of the investigated processes and the prostheses feasibility.

Keywords: Single Point Incremental Forming , Super Plastic Forming , Titanium alloy

This paper presents an example of applicability of the STEP standard in a design process of a new specific sub-assembly product in the heavy machinery industry in Serbia. We tested the interoperability of the STEP standard in several CAD systems and their compatibility and quality of conversion process. Results obtained in performed experiments demonstrate that the STEP standard offers simplified data exchange between heterogeneous CAD systems and serves not only as a tool for integration and exchange the data of products and processes, but subsequently supports the integration of companies by increasing the global competitiveness, more efficient archiving, evolving and reusing the data in a solving complex entrepreneurial and production problems worldwide.

Keywords: CAD data exchange , CAD tools , Interoperability , STEP

We present the stress analysis of a pouring concrete device. In order to test the prototype of a pouring concrete equipment composed of fivearms with hollow rectangular cross sections, an extensive study about equipment for pouring concrete has been undertaken. An upgrade of a four-arms device already existing and actually working would be developed. Tests have been performed both on the prototype of the equipment and on a virtual model of the device, performed by a 3D CAD modeler and analyzed through FEM numerical programs. During experimental tests, a laser device has measured deflections at the end of the fifth arm, corresponding to applied loads. For measuring strains in the critical points highlighted by the numerical simulation strain rosette have been employed. In both the static and the dynamic conditions, Mohr's circles have been drawn from the 3D strain state and the 2D plane stress experimental records and they have been compared with those predicted through the finite element analysis. From the comparison between numerical and experimental results, a very good correlation has been obtained for static loading to assess the soundness of the virtual model.

Keywords: Articulated device , CAD , FEM , Mohr's circle , Strain analysis

Hybrid Manufacturing (HM) is oriented to combine the advantages of additive manufacturing, such as few limits in shape reproduction, good customization of parts, distributive production, minimization of production costs and minimization of waste materials, with the advantages of subtractive manufacturing, in terms of finishing properties and accuracy of dimensional tolerances. In this context, our research group presents a design technique that aims to data processing that switches between additive and subtractive procedures, to the costs and time of product-manufacturing optimization. The component prototyping may be performed combining different stages (addiction, gross milling, fine milling, deposition…) with different parameters and head/nozzles and is able to work with different materials either in addictive, either in milling. The present paper is dedicated to introduce different strategies, or in other terms, different combinations of machining features (addictive or deductive) and different materials to complete a prototype model or mold. The optimization/analys ispiece of software is fully integrated in classic CAD/CAM environment for better supporting the design and engineering processes.

Keywords: CAD , CAM , Hybrid manufacturing , Multimaterial manufacturing , Process design

During manufacturing, porcelain whiteware changes its shape due to the sintering process. For this reason, leader companies in the field of ceramics apply strict controls on final products in order to reach high quality standards. Typically, three quality parameters are considered: drop of the bottom, bending of the rim and roundness. To date, the assessment of such parameters is still based on visual inspections and manual measurements. In the present paper, authors propose a new quality assessment procedure based on reverse engineering (RE), able to measure the most relevant quality parameters in an effective, reliable and repeatable way.

Keywords: 3D model , 3D reconstruction , 3D scanning , measurement , porcelain , porcelain tableware , quality control , quality parameters , reverse engineering , whiteware

Body scanning presents unique value in delivering the first digital asset of a human body thus resulting a fundamental device for a range of applications dealing with health, fashion and fitness. Despite several body scanners are in the market, recently depth cameras such as Microsoft Kinect® have attracted the 3D community; compared with conventional 3D scanning systems, these sensors are able to capture depth and RGB data at video rate and even if quality and depth resolution are not optimal for this kind of applications, the major benefit comes from the overall acquisition speed and from the IR pattern that allows poor lighting conditions optimal acquisition. When dealing with non-rigid bodies, unfortunately, the use of a single depth camera may lead to inconsistent results mainly caused by wrong surfaces registration. With the aim of improving existing systems based on low-resolution depth cameras, the present paper describes a novel scanning system for capturing 3D full human body models by using multiple Kinect® devices in a compact setup. The system consists of an instantaneous scanning system using eight depth cameras, appropriately arranged in a compact wireframe. To validate the effectiveness of the proposed architecture, a comparison of the obtained 3D body model with the one obtained using a professional Konica Minolta Range Seven 3D scanner is also presented and possible drawbacks are hinted at.

Keywords: 3D modelling , Body scanning , Custom Avatar , Depth Camera , Model Fitting

Modular product design is an efficient strategy to let manufacturing companies meet the customers' requirements by offering a wide variety and customization of products and significantly saving time and cost during engineering and production (Fei et al., 2011). Despite numerous approaches for function modeling and modular product design (Srinivasan et al., 2012; Eckert, 2013; Vermaas, 2013) that have been developed in the last decades, carrying out an efficient product variants' design process is still an open issue for many manufacturing companies. The proposed approaches offer numerous ways to model information about product functionality, but each approach is useful and particularly well suited for different applications and domains (Summers et al., 2013). The present research compares the existing approaches for product variants design and defines a function-based model to support product design and redesign according to a modular framework, merging qualitative technical issues with business-oriented evaluation. Such a framework has been used to develop a multiuser IT platform, composed of a knowledge-based engine and four different tools to support designers and engineers in product variants creation, management, and configuration, from product functional modeling to cost estimation and life cycle assessment. The proposed model has been tested on industrial cases in the context of household appliances. Experimental results demonstrates that, after a preliminary context analysis and a proper knowledge base creation, such a model supports a more conscious decision-making and promote collaboration within an interdisciplinary design team. Finally, the case study shows the necessity, but in the meanwhile the insufficiency, of a functional decomposition as the only representation viewpoint.

Keywords: Computer-Aided Design , Design Methods , Function Modeling , Product Family and Platform , Product Modeling

Cost estimation is a critical issue for many companies concerning both offers generation and company strategic evaluations. In this paper, a framework for early cost estimation has been proposed to some firms for an assessment of its main features. The aim of the industrial survey is to promote a discussion on the needs and the expectations regarding cost estimation in order to obtain feedbacks to be addresses in the implementation of a software tool. Gather data has led to a ranking of the main characteristics the tool should have.

Keywords: CAD , Design to Cost , Early cost estimation , Knowledge-based engineering , PLM , Product configuration

This paper deals with the use of reciprocal frames in temporary gridshell structures, such as architectural pavilions in expositions and installations. These architectural examples can benefit from the use of short, easy to handle, generally joint-free, and repeatable “modules” in order to create particular self-supporting structures. The lightweight and interwoven grid obtained by connecting short elements according to the reciprocity principle is structurally efficient and, at the same time, aesthetically pleasing, mainly due to the resulting tessellation. The paper firstly investigates the connection between efficiency and aesthetics. The last part of the paper investigates some temporary architectural pavilions from both an aesthetical and parametric point of view. In order to deepen our understanding of these structures, they are re-modelled according to a bottom-up approach by means of a constraint-based parametric CAD modeller. In this way, a reciprocal frame can be explored and modified by the parametric arrangement of its generative elements, which, like a natural organism, grows in self-generating forms.

Keywords: Aesthetics , Architectural pavilions , Natural form , Parametric modelling , Reciprocal Frame , Shell structure , Tessellation

In this research activity, a new methodology for the synthesis of hand exoskeleton mechanisms has been developed and validated through real prototypes. The innovative methodology is based on a new parallel mechanism and has been tested by building a robotic assistive device for hand opening disabilities applied to real cases. The studied robotic orthosis is designed to be a low-cost, adaptable and portable hand exoskeletons to assist people with hand opening disabilities in their activities of daily livings. As regards the methodology for the synthesis of hand exoskeleton mechanism, the authors propose to use a motion capture system to acquire the real hand phalanx trajectories and the geometrical characteristics of the patient's hand, and to use optimization algorithms to properly defines the novel kinematic mechanism that better fits the finger trajectories. The preliminary testing phase of the prototype on a single patient is concluded; currently, through the collaboration with an Italian rehabilitation center, a group of patients are testing the proposed HES methodology.

Keywords: Hand exoskeleton , Hand opening disabilities , Kinematic synthesis , Portable and wearable robotics