Assembly sequence planning starting from CAD models turned out to be a relevant task in the industrial manufacturing eld. To have a successful assembly sequence, the relations between the assembly's parts and the possible interferences during the assembly operations deserve to be investigated. In particular, the collision analysis is the phase in which the movement of each part along some directions is evaluated to assess if it is obstructed by any of the other parts, and according to which the precedence matrix is computed. A lot of work has been done to address the problem, however, existing algorithms need to be improved yet. Among the open issues, the following three result to be the most challenging: the combinatorial explosion of the problem complexity, the limited choice of the assembly directions, and the engineering meaning of parts that is not taken into account, or it is manually given in input by experts. In this paper, an automatic assembly sequence planning approach is introduced. The focus is on the collision detection and precedence analysis for engineering meaningful subassemblies, namely the axisymmetric. Information automatically extracted relying on geometric processing and engineering knowledge, such as parts features and semantic interpretation of mechanical components, is rst exploited to identify the subassemblies and, then, to choose the feasible assembly direction, as well as to treat fasteners and deformable parts in a more realistic way. An industrial CAD model of a gearbox is selected as case study to illustrate the approach, also emphasizing the importance of axisymmetric subassemblies

An urban digital twin (UDT) is the virtual representation of real assets, processes, systems and subsystems (e.g., transportation, energy distribution, water usage, population, education, health, cultural heritage, etc.) of a city. By using and integrating heterogeneous data, UDTs actually allow monitoring the current status of cities and predicting/anticipating possible complex scenarios. We focus on the design and development of the geometric layer of UDTs, that is the 3D digital representations of urban morphology and physical structures (i.e. buildings), properly enriched with heterogeneous semantic information. Our method aims to build a functional geometric model of the city, exploiting at best the available data, trying to achieve a representation that is able to support geometry-related queries.

The work here presented is part of a wider research project aimed at extracting and using in industrial applications high level semantic information from 3D product models that are described by means of their boundary representation (B-rep). The specific focus of the paper is the recognition among the components of the CAD model of an assembly of those belonging to some categories of standard parts largely employed in mechanical industry. The knowledge of these components is crucial to understand the structure of mechanical products as they have specific meaning and function. Standard parts follow international standard in shape and dimensions, and also typical mounting schemes exist concerning their use in the product assembly. These distinctive features have been exploited as a starting point to develop a multi-step recognition algorithm. It includes a shape-based and a context-based analysis both relying on the geometric and topological analysis of a CAD model. As already anticipated by Voelcker in his visionary ability to anticipate open challenges, the shape of an object alone is not enough to understand its function. Therefore, context assessment becomes crucial to validate the recognition given by the shape-based step. It allows to uniquely recognize components in mechanical CAD models, by confirming correct results, refusing the false positives, as well as choosing the correct one when the assignment is multiple.

Design For Assembly (DFA) aims at improving product design facilitating assembly phases via the application of evaluation metrics and design guidelines. However, DFA analyses are usually performed manually and the adoption of supporting tool is poor. This paper investigates the application of algorithms allowing to extract from CAD assembly models the required data to perform automated DFA analyses, thus providing a tool to support designers' everyday works. In particular, attributes from geometric feature recognition algorithms, solids properties and assembly parts' semantics are leveraged and mapped to the parameters required to accomplish DFA evaluations. The proposed approach is illustrated on a 3D printer for home use. At first, a manual DFA analysis has been performed on the product identifying product BOM, components properties, assembly cycle and times according to models in the literature. Then, the CAD model of the printer has been processed with some geometric algorithms to verify the possibility to extract the required data to be used as input to the DFA analysis. The test case has demonstrated the feasibility of the approach, even if some design considerations and improvement directions still need the critical evaluation of the designer.

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Focus of this work is the recognition of the standard parts contained in a CAD assembly model, with the aim of enhancing the model semantics. Standard parts are components typically used in mechanical industry, which have a specificc engineering meaning and follow international standards. In particular eight categories of standard parts are considered, i.e. screws, nuts, O-ring, washers, circlips,keys, studs and pins. The provided algorithm relies on the geometric and topological analysis of the CAD model parts. A part is assigned to one of the categories if it satisfies the geometric requirements extracted for that specific category, based on engineering knowledge and design rules. In addition, if a part is recognized as standard part, besides the class of membership, further information is provided as result, namely its engineering dimensions.

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Mechanical assemblies are very complex structures, made of many parts of various shapes and sizes with different usages. Consequently, it ischallenging to manage them during all the manufacturing processes, from the design to the assembly and the recycling. Aiming to simplify theassembly structure and reduce the number of parts to deal with simultaneously, in literature many works exist on subassemblies identificationstarting from the CAD assembly model. However, the methods provided loose sight of many details associated with the parts, as well as the factthat the treated model represents a real mechanical assembly which respects precise engineering rules. At this regard, this work introduces a novelmethodology to detect meaningful clusters in CAD assembly models. The logic applied relies on engineering knowledge, both of mechanicalassemblies' components and of assembling techniques, and on the leveraging of the semantics of components. In particular, referring to generaldesign rules, we have identified some heuristics to exploit to partition the assembly into different types of clusters, such as the symmetry alongan axis and the presence of fasteners or welds. It results that the assembly's parts are meaningfully grouped, considering, at the same time, theirshape, functionality, and type of contact.

In industrial manufacturing, both in the design and the production phase, the management of modern mechanical assemblies is becoming demanding due to their increasing complexity. The use of stable subassemblies concept constitutes a better alternative, which allows to independently treat smaller groups of the assembly's parts, also to achieve a parallel production. At this regard, several methods for automatic subassemblies identifi-cation, starting from the assembly CAD model, have been provided. However, most of the methodologies proposed rely on human intervention, especially in the model processing to make available essential data, while other details are ignored. After giving the definition of stable subassembly, this paper focuses on the application of stable subassemblies identification to industrial CAD models and highlights the issues arising. With the aim of ensuring a reliable CAD model analysis, starting point of the identification, the possible real engineering situations, both related to assembling methods and modelling techniques, are presented. Ap-proaches to algorithmically address them are then described, with the help of two examples of mechanical assemblies.