Geometric modeling and processing

In this paper the authors will describe the work which the University of Florence and IFAC-CNR (Florence) have performed in order to design an innovative platform for High-latitude LDB flights based on multi-experiments and versatility concepts. In order to satisfy the functional requirements and difficult structural constraints in terms of stiffness, strength and weight, the authors will describe an innovative approach to designing the gondola using problem-solving techniques, virtual prototyping and topology optimization in a systematic way. By means of these tools, a set of optimized geometries has been tested, starting from the first implementation of the BarSPOrt experiment's platform. Some of these solutions will be described.

In addition to stepping through the typical hardware parts of an Attitude Control System borne for stratospheric platform, the paper describes some fast position sensors. The use of two axis magnetometers at high latitude, even though with a lower accuracy, is analyzed. A high-accuracy motorized sun tracker based on a Position Sensitive Detector photodiode capable of driving the gondola in pointing or scanning mode in any given arbitrary anti-sun direction is also presented. Lastly, as an important part of the entire sensor development project, the paper describes a simulation of the thermal behavior of a pressurized cylinder in which electronic photosensitive devices and a CPU system are housed. To employ electronic device built within a commercial temperature range and intended to stay on the ground, it is extremely important to have a pressurized and conditioned environment in order to avoid a reduction in the performances of some ACS components.

This paper describes a method for the recognition of the semantics of parts (features) of a component from a pure geometric representation. It is suitable for verifying product life-cycle requirements from the early stages of the design process. The proposed method is appropriate to analyse B-rep geometric models, and it is not limited to models described by planar and cylindrical surfaces, but it can handle several types of face shapes. In this work the concept of semanteme is introduced. A semanteme represents the minimal element of engineering meaning that can be recognised in a geometric model. The semantemes recognised in a part of the model, which are potentially of engineering significance, are used to associate an engineering meaning to the part. This approach gives a wide flexibility to the proposed system, which is suitable to be used in different contexts of application, since it is possible to describe the reference context using the semanteme that the system can manage. In the paper the implemented prototype system is briefly described. The prototype system takes advantage of neutral interfaces that allow geometrical and topological information to be retrieved from a commercial CAD system. © 2003 Elsevier Ltd. All rights reserved.

Keywords: Feature recognition , Intermediate geometric model , Semantics recognition

Virtual prototyping of cloth has recently become a topic of increasing interest both in computer graphics and computer-aided design for industrial fabric or apparel production. Aiming at an accurate simulation of garment shapes, this paper presents a physics-based system for virtual cloth modelling, specifically conceived for design purposes and targeted to the clothing industry. This environment should allow the designer/modellist to validate her/his style and design options through the analysis of garment virtual prototypes and simulation results in order to reduce the number and role of physical prototypes. To this end, a complete physics-based model has been defined, oriented to actual complex-shaped apparel, incorporating aspects related to garment's shape and structure (e.g., 2D profiles of basic patterns and multi-layered parts), mechanical/structural properties of fabric materials and multi-layered parts, and design/manufacturing processes (e.g., ironing, starching). The physical garment's model has been developed upon a particle-based model embedded in constrained Newtonian dynamics with collision management. The system has been validated within European and national projects, simulating several female and male garments with different levels of design complexities and directly provided from involved clothing companies. © 2004 by CAD Solutions Company Limited.

Keywords: Garment design and manufacturing , Garment simulation , Physics based-models

This paper presents a 3D optical digitiser based on an active stereo vision aproach. The system is composed of a digital camera, a multimedia projector and software to control the hardware and process the images. The proposed solution integrates an active coded light method with a photogrammetric procedure in order to allow the acquisition of complex surfaces. In the work, experimental tests have been conducted with a nominal model and styling components of two-wheeler vehicles. The measurement process and the experimental results have been analysed to verify usability and accuracy of the methodology.

Keywords: Coded light , Photogrammetry , Reverse Engineering , Stereovision

The planning of the hip prosthesis surgical operation is usually performed manually by the surgeon, who 'draws' on a patient's X-ray image the outline of the prosthetic stem in order to choose the one most suitable for the case at hand. In an attempt to give some repeatability and objectivity to the planning phase, a procedure has been devised for hip prosthesis' stem selection based on the extraction of the femoral relevant outlines. This work presents a computer aided method aimed at automatically extracting the medulla duct outlines from a human femur radiographic image. The outlines are retrieved by referring to a suitable geometric model of the generic femoral cross-section; the projection function obtained by simulating the radiographic acquisition of such a model is fitted on the grey-level functions corresponding to the rows of the actual digitised radiographic image by means of a least squares algorithm. The resulting outlines are used in a software tool performing the hip prosthesis pre-operational planning. © 2003 Published by Elsevier B.V.

Keywords: Medical images processing , Model-based image processing , Surgery aiding tools

Vehicle noise and vibration levels are basic parameters in passenger comfort. Both static and dynamic stiffness of sheet metal parts is commonly increased by means of stiffening ribs. Vibrations are also reduced by adding a layer of damping material on the floor, the roof, the firewall and other parts of the vehicle. In common practice the panels to be treated are ribbed according to criteria based on the designer's experience, rather than on well defined design procedures and are uniformly covered by a layer of damping material. However, these are not efficient design solutions, especially with regard to the effectiveness of vibration reduction and to weight containment. In this paper a novel approach to achieve an optimal distribution of stiffening ribs and damping material will be presented. The proposed method is based on a Genetic Algorithm (G.A.) procedure which takes into account both the vibroacoustic performance and the weight and cost reduction. A simple case study will be illustrated to demonstrate the Capabilities of the developed procedure.

As known, incremental forming is a flexible and innovative sheet metal forming process which allows complex shape shells forming without the need for any die. For these reasons, incremental forming is nowadays suggested for rapid prototyping and customised products. The present paper is focused on material formability in incremental forming and, in particular, on the evaluation and compensation of elastic springback. The latter significantly modifies the imposed shape. For this purpose, a deeper assessment of the process was developed following three different approaches. First of all, a wide experimental investigation on the influence of some relevant process parameters was developed. At the same time, an explicit FEM analysis of incremental forming process was carried out in order to verify its effectiveness and, as a consequence, its ability to be used as a design tool. Furthermore, the obtained parts were analysed by a reverse engineering technique and the measured geometry was numerically compared with the desired one, with the aim to quantify the geometrical discrepancies. In this way, an integrated numerical/experimental procedure is proposed in order to limit the shape defects between the obtained geometry and the desired one. © 2004 Elsevier B.V. All rights reserved.

Keywords: FEM , Geometrical accuracy , Incremental forming

Incremental forming is nowadays increasing its presence in industry as a new but interesting process, especially for production of small batches or unique components. Anyway, relevant efforts have to be spent in order to reduce the typical incremental forming processes drawbacks that risk to belittle the high advantages in terms of costs and simplicity. In fact, the process duration, usually equal to several minutes even if the operations are carried out on high speed numerical controlled units, and a certain tendency to produce no precise parts, can reduce industrial interest about incremental forming. A possible strategy to reduce the latter item is the design of modified trajectories able to take into account both the springback effects and the stiffness reduction due to the particular clamping equipment. In this paper the above introduced strategy is pursued integrating an on-line measuring system, based on a digital inspector, and a CNC open program. The actual geometry is acquired in some remarkable points and a compensation routine modifies the coordinates of the future punch path. The modification policy has been developed by using an effective FE code. An experimental verification shows the good potentiality of the suggested methodology.

In the fields of industrial design and car manufacturing the creation of 3D curves plays a fundamental role within the design process: it allows the improvement of the visual appeal of artifacts, it enhances ergonomics and the product's commercial competitiveness through product differentiation. When flexibility and intuition are to be privileged it is fundamental to achieve natural, intuitive, mathematically correct, creation and modification of surfaces. The scientific aim of this research is the development of an innovative metaphor to modeling of 3D curves which maintains the natural expertise of the designer. The major contribution of this paper is the capability of the system to create and modify the curve naturally, without mathematical artifices, within the limits set by the use of Bezier curves. The proposed metaphor combines the benefits of two acknowledged techniques referred to as the Digital Tape Drawing and the Eraser Pen, which allow the real-time modification of the curve. The integrated adoption of tangible interfaces and innovative mathematical tools, combined with the adoption of semi-immersive environment and lightweight interaction devices, delivers intuitive curve creation for free-form modeling within the virtual scene. The paper describes the details of the algorithm developed and it highlights its strengths during the styling phase. © 2004 ACM.

Keywords: 3D curve generation , Computer aided styling (CAS) , Virtual environments

Reverse engineering techniques are broadly used in the development process of products with meaningful aesthetic properties. Many stylists prefer to evaluate the product shape on the basis of a full-scale hand made physical mock-up. Such model has then to be converted into a 3D CAD model, to begin the product engineering and production processes. A critical aspect of the RE process is that the physical mock-up, made by the stylist, usually does not take into account the engineering production constraints. The surface reconstruction activity must then be followed by a modelling phase, where the engineering designer modifies the reconstructed model shape in order to make it suitable for production. At the end of this process, no matter how accurate and precise the surface reconstruction phase has been, the product model will be different from the original mock-up, and then it needs to be submitted to the stylist for the validation of its shape. For the stylist, getting used to working with physical models, the shape validation on a virtual model is not a trivial task. The objective of this research is to develop a software tool to support the identification of aesthetic and functional regions of the product model shape, that have been modified with respect to the original mock-up. The proposed approach is based on the decomposition of a 3D surface analysis problem into a simpler 2D curves analysis problem. This approach simulates the traditional method used by stylists to evaluate the quality of shapes. The implementation of the developed algorithms has been performed using a commercial software package (I-deas FreeForm by EDS/Unigraphics) and it has been successfully applied on real test cases. © 2003 Elsevier Ltd. All rights reserved.

Keywords: Physical mock-up , Product engineering , Style , Virtual mock-up

The use of 3D tracking systems in a Virtual Reality environment may definitely change CAD interfaces and free-form surface modelling. In this paper an original method for full 3D interactive surface shaping and modifying is described. VISM (Virtual Integrated Surface Modeller) has been developed with the leading idea that 3D tracking system can dramatically speed up modelling sessions. On the opposite of a W-I-M-P (Windows-Icons-Menu-Pointer), paradigm common to most current CAD systems, VISM demonstrates that Virtual Reality devices can manage all types of surface in a unique shape generative action. Unlike "Virtual Clay" based and "Metaball" modelling techniques, VISM both wants to give to engineers and designers a more intuitive and natural tool to get 3D shapes. Based on Polhemus Fastrak and stereoscopic vision, VISM doesn't provide icons to (he designer, leading to a "null icons" and "null menu" full 3D interface. The new interface is fully implemented on bi-manual input system on top of a Virtual Reality environment. The entity grabbing is also supported by pinch-enabled gloves. The designer exploits a NURBS curve tool to deform a NURBS surface and extracts drive curve direction from his right hand movement. The curve tool may be also real-time deformed with left hand through node-control point repositioning. Furthermore the modeller is fully implemented using NURBS curves and surfaces and a fast surface-over-curve positioning and deformation has been implemented, replacing both traditional snapping and picking activities.

Keywords: 3D interface , CAD , Spatial Tracking , Surface modelling , Virtual Reality

The reuse of free-form surface features (FFF), created in different design sessions, is a growing research field in geometric modelling. The development of this research field will give important improvements in surface shape activities in modern CAD and CAID (Computer-aided Industrial Design) systems. Traditionally, the surface modelling software has been founded on parametric definition of curves and surfaces (Splines and NURBS), giving to designers a great flexibility and power, but lacking in global shaping tools. Nowadays, the most exploited modelling commands are curve-constraining rules and control points repositioning: the first is very time-consuming, while the second is not global and may lead to a smooth-less surfaces. In this paper, we investigate on an application of Multiresolution Analysis (MRA) theory in wavelets representation, to develop a innovative global shaping tool for free-form features reusing. The developed algorithm aims to overcome the traditional control points description thanks to a wavelets coefficients representation of geometry features. The final result of this approach is to give the possibility in building a designer's own features library, which can be available in different modelling sessions, both improving surface quality and reducing time-consuming shaping procedures in product design development.

Keywords: Free-form features reuse , LOD , Multiresolution , Wavelets

An integrated environment based on CAD assembly software and on an Augmented Reality wearable system is used to improve the overall integration between engineering design and real prototypes manufacturing. The environment following called - Personal Active Assistant (PAA) - exploits a CAD tool connection to remarkably improve object recognition, best assembly sequence optimization, and operator instructions generation. PAA is real-time and wirelessly linked to a remote server or designer workstation where project geometric database is stored. The PAA head-mounted camera is also able to acquire the human-driven assembly sequence and check the efficiency and correctness via object recognition: an incremental sub-assembly detection algorithm has been developed in order to achieve complex dataset monitoring. On the other hand, the Augmented Reality-based assembly evaluation tool allows engineers to interact directly with the assembly operator while manipulating the real and virtual prototype components. Information from the assembly planner can be displayed, directly superimposed, on the real scene by using a see-through head-mounted display. Thus the new combined software and hardware equipment may be considered a step ahead in the support of true concurrent engineering and remote collaboration, strongly improving this latter through a better heterogeneous task integration. Several tests have been performed also to achieve personnel training and warehouse part seeking.

Keywords: Assembly , Augmented reality , CAD , Concurrent engineering , Virtual reality

The presence of fillets, rounds, chamfers and grooves is typical of many real-world mechanical components. Such features introduces in the model various topological and geometrical modifications which may alter the correct understanding of its main features. Another drawback which hinders the correct engineering evaluation of a part is that its geometrical and topological representation is not unique, since it depends either on the different procedures used to generate CAD models or on the different internal representation of the geometric kernels used by CAD packages. The overall aim of this work is to define an intermediate representation scheme which incorporates information about minor features such as chamfers, fillets, rounds and grooves into a graph based representation and overcomes the problem of non-uniqueness in the geometric representation. The representation scheme discussed here takes as input a solid model in B-rep form, and provides a description of a part at an higher level of abstraction in comparison with the raw B-rep description. A procedure for secondary features recognition is also described in this paper. The proposed algorithm consists of two steps where both topological/geometrical properties and dimensional attributes are investigated in order to fulfil a correct recognition. The recognized secondary features are then inserted into the model as labels which qualify the relationships between the faces of the graph representation. The resulting modelling scheme can be conveniently used for primary feature recognition as well as for other engineering analysis/simulation purposes. © 2003 IEEE.

Concurrent Engineering methodology and process analysis and modeling showed the importance of tools that allow the designers to evaluate, from the beginning, different aspects of product definition. 3D CAD systems, simulation tools and virtual prototyping technologies can support the designer during her/his decision-making activity but, in order to provide an effective support, they must be tailored to the needs of the design process of each specific product. During last years, different types of tools appeared on the market to support this tailoring activity and to promote the development of product-dependent applications. In this paper, we have focused the attention on software tools named KAE (Knowledge Aided Engineering) development shells. Applications implemented by using this type of tools can support experts during the decision making process to evaluate alternative solutions. They provide a kernel for the integration of different technologies, and represent a basic step for the development of the product design. In this paper we present a brief overview of the architecture of a typical KAE application and we provide a survey of the most significant systems that we have developed, within different application domain, taking advantage of the KAE technology. © 2003 by Springer Science+Business Media New York.

Keywords: Feature technology , Knowledge aided engineering

Collaborative solid modelling among distributed designers is becoming an effective chance for product design. Nevertheless the available solutions usually rely on proprietary systems and formats and do not enable heterogeneous collaboration. The overall aim of the work presented in this paper is to introduce a frame-work for heterogeneous collaboration. The proposed solution is based on the definition of an intermediate neutral modelling language capable of capturing the modelling activities carried out by distributed users. The described system is based on the XML Schema technology.

Commonly, during the aesthetic design process, stylists sketch features called character lines over a simple and "uninteresting" geometry (e.g. a car bonnet) in order to confer personality, emotional feeling and style. This work presents an original interface paradigm for character line sketching in a virtual reality environment. Taking advantage of the 3D interface, the feature path, also called leading line, can be directly sketched on the initial surface by realtime projection. Afterwards, a semi-transparent section is selected along the path in a interactive way and then the feature profile is sketched on this plane according the user's intention. Subsequently, by moving the virtual pen forwards along the path, the character line is generated, on the contrary if the pen is moved backwards the feature is partially erased. The distance of the virtual pen from the leading line controls, in real time, the offsetting along the path of the feature which remains consistent in style and identity. Such a system has been proven to be a powerful tool for fast expression and evaluation of ideas, which can be, in subsequent design phases, integrated with detailed surfacing applications and prototyping.

Keywords: Constrained-based design , Curve and surface design , Feature-based design , Parametric modelling

The development of extremely high performance aerospace power transmissions will be a very interesting technological challenge for the next future. In gear design for high power transmissions, desirable characteristics, such as low noise emissions, low vibrations, minimum size, minimum maintenance cost, but most of all minimum weight can be obtained through the development of innovative layouts. However, most of the rules based on experimental data, by which common gears are calculated and verified, are not applicable to transmissions which can be defined unconventional in terms of geometry and/or operating conditions (high power, high rotating speed, low weight). In these cases, numerical simulations can be performed by using FEM codes. The objective of this work is to describe how integrated CAD/FEM tools can be employed to develop procedures for the static performance analysis of unconventional gears. In the paper, potential characteristics, limits and capabilities of simulating real system behaviours are discussed.

Keywords: Computer aided design , Finite element method , Gear design

A CAD method for the checkout and design of Belleville springs is presented. The method eliminates the need to resort to conventional trial-and-error techniques. In a matter of seconds, it rapidly and accurately checks out and designs Belleville springs, outputting the load-deflection characteristics in graphic and table formats and can generate a dimensioned drawing. To enable the designer to work in the same environment, the software has been provided with a user-friendly interface for fatigue calculation along with the characteristics of parallel/series assemblies. The algorithms developed and used for each calculation module are illustrated.