Geometric modeling and processing

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 stylistic design of new industrial products often starts from shaded handmade sketches which, usually, need to be converted into 3D digital models by using CAD software packages for the subsequent design phases. This conversion often represents the bottleneck of the whole development process. Shape from Shading (SFS), which attempts to recover the 3D geometry of an object starting from a single shaded representation, is potentially capable of speeding-up the 3D conversion. However, existing approaches prove to be extremely unstable and error prone mainly due to the under-determination of the SFS problem. In order to increase the performance of shading based reconstruction authors propose a step-by-step variational-based approach. In particular, the problem is solved into multiple steps, each one providing the initialization for the following, so that the solution gradually converges towards the final surface. Tested against a set of case studies, the method proved its effectiveness.

Keywords: 3D design , Computer aided design , Numerical optimization , Shape from shading , Stylistic content , Variational approach

Minimization techniques are widely used for retrieving a 3D surface starting from a single shaded image i.e., for solving the shape from shading problem. Such techniques are based on the assumption that expected surface to be retrieved coincides with the one that minimize a properly developed functional, consisting of several contributions. Among the possible contributes defining the functional, the so called "smoothness constraint" is always used since it guides the convergence of the minimization process towards a more accurate solution. Unfortunately, in areas where actually brightness changes rapidly, it also introduces an undesired over-smoothing effect. The present work proposes two simple yet effective strategies for avoiding the typical over-smoothing effect, with regards to the image regions in which this effect is particularly undesired (e.g., areas where surface details are to be preserved in the reconstruction). Tested against a set of case studies the strategies prove to outperform traditional SFS-based methods.

Keywords: 3D model , Minimization , Shape from shading , Smoothing , Smoothness constraint , Variational approach

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.

The work described in the paper is motivated by the lack of computer-aided tools to support Product Planning and, more specifically ideation processes of New Product Development (NPD) initiatives. The domain is populated by software applications aimed at managing and organizing Product Planning activities, which thus poorly contribute to the definition of new product characteristics, and models to stimulate novel ideas. The latter face limitations in terms of overlooked implementation with CAD tools supporting the following NPD phases and poor exploration of the design space. The authors propose an original method and software prototype capable to provide a wide range of stimuli, whose testing demonstrated much better results than traditional approaches in terms of quantity and variety of generated ideas.

Keywords: CAD , idea generation , New Product Development , product attributes , Product Planning , Value Dimensions

A methodology for integrating the CAD-CAE design of a chain drive system is presented by evaluating meshing angles. The methodology correlates the angles of engagement with transverse vibrations and the tensile force of the chain links, showing that the dynamic behaviour of a chain drive can be significantly improved by fine tuning the meshing angles. An objective parameter was introduced to evaluate divergence from correct meshing. Here the methodology is applied to optimize the timing chain system of a high power V12 quadruple overhead camshaft engine. The reliability of the method relies on multibody modelling all the components and accurate experimental tests. Correlating the experimental measurements provided exact modelling of the contact forces, exact evaluation of stiffness and damping values and precise dynamic modelling of the tensioners and guides. Finally, the dynamic performance of the two different primary stage chain drive layouts were compared.

Keywords: Chain stiffness , Contact force model , Meshing impact , Multibody dynamics , Tensioner , Transverse vibration

Foams are able to absorb energy and bear stress more uniformly and efficiently than the correspondent bulk materials. This makes them ideal candidates to increase the specific structure's absorption efficiency.Concerning their characterisation, there are still some open issues needing further investigations, such as the experimental analysis of their dynamic behaviour with alloy types, strain rates and foam density changes.This paper focuses on the above mentioned issues presenting the results of a dynamic characterisation by means of a direct tension-compression Hopkinson bar. Tests are carried out on AlSi7 alloy foam specimens obtained from a large ingot made by compact powder technology. The results are discussed mainly in terms of strength and energy absorption efficiency, considering the effects of strain rate and of the variation of foam density, due to the manufacturing process.

Keywords: Aluminium foams , Dynamic crushing , Hopkinson bar , Mechanical characterisation

Despite of the widespread of annotated 3D virtual models, it is still important to produce engineering drawings for a correct communication among the people of the design and manufacturing chain. Automatic drafting through meta drawing definitions, called Drafting Schemes, is proposed in this paper to save time when drawing becomes a repetitive task. The approach produces drafts with a predetermined content in terms of views arrangement and dimensioning strategy, and guarantees robust results to the variations of the input geometry. In fact, the geometrical entities referenced by the generated dimensions are retrieved through dedicated search algorithms based on recognition of geometric features of the input model. The approach has been implemented and tested on a family of gear motors showing feasibility and good results in terms of drafting time savings.

Keywords: Design Automation , Drafting , Feature Recognition , Knowledge Based Systems

Technical knowledge and experience are intangible assets crucial for competitiveness. Knowledge is particularly important when it comes to complex design activities such as the configuration of manufacturing systems. The preliminary design of manufacturing systems is subject to a huge variability of inputs and outputs and involves decisions which must satisfy many competing requirements. This early engineering phase relies mostly on experience of designers and engineers and is associated with long lead times and high probability of mistakes. Knowledge-Based Engineering (KBE) and knowledge representation techniques are considered to be a successful way to tackle this design problem at an industrial level. This paper presents a methodology to support the configuration of powertrain assembly lines, reducing design times by introducing a best practice for production systems provider companies. The methodology is developed in a real industrial environment, introducing the role of a knowledge engineer. The approach includes extraction of existing technical knowledge and implementation in a knowledge-based software framework. The framework is then integrated with other software tools allowing the first phase design of the line including the line technical description and a 2D and 3D CAD line layout. The KBE application is developed and tested on a specific powertrain assembly case study for which existing knowledge is collected, formalised, implemented in the application and integrated with existing tools. Finally, the paper presents a first validation among design engineers, comparing traditional and new approaches and estimating a cost-benefit analysis useful for future possible KBE implementations.

Keywords: Design automation , Knowledge acquisition , Knowledge-based engineering , Powertrain assembly lines

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.

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

Persian architecture is characterised by shapes and patterns, which can be analysed through mathematical models. Beside 2D patterns, many of the traditional geometric ornaments are realised on 3D surfaces such as domes or vaults. Literature mainly addresses the 3D problem by means of a 2D scheme, which is an important and synthetic representation but is not exhaustive and lacks of clarity. This paper proposes a framework based on the integration of 2D drawings, as in the traditional approach, and a photogrammetric 3D model based on a sample of standard resolution images (tourist pictures). The framework is tested on a muqarnas, a characteristic Persian ornament, in order to study and analyse its modular design and hierarchy of elements. As a case study, the entrance iwan of the Shah Mosque in Isfahan, Iran, is considered. The result is a link between the 3D patterns and the geometry of architectural elements, which completes and overcomes their schematic 2D representation.

Keywords: CAD modelling , Geometric analysis , Iwan , Modules , Muqarnas , Persian ornament , Representation of architecture

A significant interest exists in measuring the thermal emissivity of building surfaces since high values combined with high solar reflectance allow rejecting solar energy absorbed by irradiated surfaces, whereas intermediate or low values permit to limit condensation of humidity, heat loss to the sky, or heat transfer through airspaces. The most used measurement method is probably that described by the ASTM C1371 Standard, which correlates the thermal emissivity to the radiative heat flux exchanged in the infrared between the sample surface, kept at ambient temperature, and the bottom surface of a hot emissometer head. With samples showing a low thermal conductivity, the 'slide method' modification is generally used: the hot head is allowed to slide above the sample in order to prevent this from warming up. The slide movement, however, is carried out by hand and time is needed to achieve a stabilized output, therefore the measurement may be time-consuming and also affected by the operator. In order to solve both problems, an automated approach is proposed here, in which the head is moved by the arm of a robot. This manages either the slide movement or the calibration with reference samples, interacting with a computerized data acquisition system that monitors the emissometer output.

Keywords: Cool roof , Emissivity , Emissometer , Infrared emittance , Infrared radiation , Measurement , Slide method , Thermal emittance

A 3D automatic facial expression recognition procedure is presented in this work. The method is based on point-by-point mapping of seventeen Differential Geometry descriptors onto the probe facial depth map, which is then partitioned into seventy-nine regions. Then, features such as mean, median, mode, volumes, histograms are computed for each region and for each descriptor, to reach a varied large set of parameters representing the query face. Each set of parameters, given by a geometrical descriptor, a region, and a feature, form a trio, whose featuring numerical values are compared with appropriate thresholds, set via experimentation in a previous phase by processing a limited portion of the public facial Bosphorus database. This allows the identification of the emotion-based expression of the query 3D face among the six basic ones (anger, disgust, fear, joy, sadness, surprise). The algorithm was tested on the Bosphorus database and is suitable for applications in security, marketing, medical. The three-dimensional context has been preferred due to its invariance to different lightening/make-up/camouflage conditions.

Keywords: 3D face , Differential geometry , Emotions , Face expression recognition (FER) , Facial expression recognition , Shape index

This study proposes a novel approach to automatically localise 11 landmarks from facial RGB images. The novelty of this method relies on the application, i.e., point-by-point mapping, of 11 differential geometry descriptors such as curvatures to the three individual RGB image components. Thus, three-dimensional features are applied to bidimensional facial image representations and used, via thresholding techniques, to extract the landmark positions. The method was tested on the Bosphorus database and showed global average errors lower than five millimetres. The idea behind this approach is to embed this methodology in state-of-the-art 3D landmark detection methods to accomplish a full automatic landmarking by exploiting the advantages of both 2D and 3D data. Some landmarks such as pupils are arduous to be automatically extracted only via three-dimensional techniques. Thus, this method is intended as a bridging-the-gap preliminary technique that takes advantages of 2D imaging only for integrating advanced landmark localisation methodologies.

Keywords: Differential geometry , Face analysis , Facial landmarks , Landmark localisation , RGB images

Digital documentation and high-quality 3D representation are always more requested in many disciplines and areas due to the large amount of technologies and data available for fast, detailed and quick documentation. This work aims to investigate the area of medium and small sized artefacts and presents a fast and low cost acquisition system that guarantees the creation of 3D models with an high level of detail, making the digitalization of cultural heritage a simply and fast procedure. The 3D models of the artefacts are created with the photogrammetric technique Structure From Motion that makes it possible to obtain, in addition to three-dimensional models, high-definition images for a deepened study and understanding of the artefacts. For the survey of small objects (only few centimetres) it is used a macro lens and the focus stacking, a photographic technique that consists in capturing a stack of images at different focus planes for each camera pose so that is possible to obtain a final image with a higher depth of field. The acquisition with focus stacking technique has been finally validated with an acquisition with laser triangulation scanner Minolta that demonstrates the validity compatible with the allowable error in relation to the expected precision.

Keywords: Cultural heritage , Focus stacking , Photogrammetry , Small artefacts , Structure from motion

The present work aims at the development of an advanced control system implemented through Adams/View-Matlab/ Simulink co-simulation for a high-performance motorcycle dynamics study. In particular, the purpose of this study is to create a model able to consider several aspects of the rider-motorbike dynamic simulation and its control system, generally treated separately in the literature, making also use of an original and accurate modelling of the rider. From a previous multi-body model of motorcycle/virtual rider, developed by the authors, a flexible tool is created to simulate system dynamics to follow any trajectory at a prescribed velocity profile. Considering high-performance motorcycle dynamics are greatly influenced by the rider's weight, his movements have been accurately replicated to obtain the most realistic results. To simulate the passive impedance of rider's arms, a torque was applied to the steering as per the literature. The aerodynamic force was modelled as a function of kinematics variables and rider's posture. The control system is very flexible and adaptable to different manoeuvres realistically reproducing engine and braking performance, steering torque and rider movements. Numerical results show that the control system can accurately direct the motorcycle/ rider system along an entire lap of the Monza circuit, following a desired path at a given velocity profile. The model developed allows a complete view of the motorbike-rider dynamic behaviour thus being useful during both design phase and set-up, with a considerable saving in terms of both cost and time; it can also evaluate the influence on the system dynamics of riders with different anatomical characteristics and driving styles.

Keywords: Co-simulation , Control , Multibody , Path tracking , Rider/motorcycle