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International audience; The functional tolerancing of hyperstatic mechanisms provides contractual documents established following the ISO tolerancing. The tolerancing methodologies consider that the mechanism is infinitely rigid. These mechanisms impose tight clearances to ensure the functional requirements and parts fittability. The proposed methodology consists in developing a mechanical model relating the tolerances obtained by traditional methods of geometrical tolerancing and the parts deformability to define the tolerance values of the geometrical specifications. The first step is to define the geometrical specifications with ISO tolerancing. The fittability between two parts in contact requires maximum material conditions. The functional requirements employ least material condition. The second step consists in defining the capacity of parts to deform taking the tolerance values into account. A mechanical model is described relating the parts deformability to the tolerances to guaranty the conformity of the functional requirements and assembly parts fittability. As a validation example, the proposed methodology is used on a hyperstatic mechanism composed of two subassemblies: an outer tube and a shaft made of several assembled sections.

International audience; When manufactured parts undergo large deformations during the manufacturing process, the global specifications of a part based on the concept of tolerance zone defined in the ISO 1101 standard [1] enable one to control the part's global defects. However, the extent of this tolerance zone is too large when the objective is to minimize local defects, such as hollows and bumps. Therefore, it is necessary to address local defects and global defects separately. This paper refers to the ISO 10579 standard [2] for flexible parts, which enables us to define a stressed state in order to measure the part by straightening it to simulate its position in the mechanism. The originality of this approach is that the straightening operation is performed numerically by calculating the displacement of a cloud of points. The results lead to a quantification of the global defects through various simple models and enable us to extract local defects. The outcome is an acceptable tolerance solution. The procedure is first developed for the simple example of a steel bar with a rectangular cross section, then applied to an industrial case involving a complex 3D surface of a turbine blade. The specification is described through ISO standards both in the free state and in the straightened state.

In the last few years the need for methodologies capable of performing an automated geometric inspection has increased. These methodologies often use 3D high-resolution optical digitisers to acquire points from the surface of the object to be inspected. It is expected that, in the near future, geometric inspection will be requiring more and more the use of these instruments. At present geometric inspection is not profiting from all the opportunities attainable by 3D high-resolution optical scanners or from the numerous tools which can be used for processing the point cloud acquired from the inspected product. For some years now, these authors have been working on a new methodology for automatic tolerance inspection working from a 3D model acquired by optical digitisers. In this paper all the information recognisable in a scanned object is organised into a new data structure, called Recognised Geometric Model (RGM). The final aim is to define a representation of the inspected object for the automatic evaluation of the non-idealities pertaining to the form, orientation and location of the non-ideal features of the acquired object. The key concept of the proposed approach is the capability to recognise some intrinsic nominal properties of the acquired model. These properties are assumed as references to evaluate the non-idealities of the inspected object. With this approach the references of geometric inspection are searched for in the inspected object independently of a tolerance specification and of the availability of a 3D nominal representation. The high-level geometric information within RGM depends on the rules used for its identification. The capability to recognise specific categories of nominal references offers the possibility of introducing new tolerances to be specified. The proposed approach has been implemented in original software by means of which a specific test case has been analysed.

Purpose: For some years now, our research group has been developing a new methodology for automatic tolerance inspection starting from an acquired high-density 3D model. In this paper, with a view to grouping together all the information recognisable in a scanned object, a new data structure, called Recognised Geometric Model (RGM), is proposed. Based on this data structure the evaluation of the non-idealities of the acquired object (form, orientation and location non-idealities) can be automatically carried out. Method: RGM is the result of an approach founded on the concepts of non-ideal feature and intrinsic nominal reference. The object to be inspected is segmented into a set of non-ideal features and, for each of them, one or more intrinsic nominal references are identified. An Intrinsic Nominal Reference is detected when a geometric property was recognised to be common to a set of adjacent points in the 3D data set representing the acquired object. The recognition of these references from a scanned object is carried out based on some rules which, therefore, play a leading role in the definition of the domain of the representable entities within RGM. Result: New and old categories of form non-idealities are here defined and some procedures are proposed for a more robust process of verification of traditional tolerance categories (such as the straightness of a cylinder generatrix). Discussion & Conclusion: When using the RGM, tolerances can be specified according to the set of available and recognisable intrinsic nominal references. This allows the automatic geometric inspection of the workpiece. However, the approach here proposed does not rule out the possibility of querying the RGM data structure by explicit geometric product specifications, in order to gather some quantitative information concerning special intrinsic geometric parameters and/or non-idealities.

Automating completely the process of geometric errors verification has some problems. The most criti-cal ones are the preventive shape recognition and the lack of an agreement about criteria to be used to associate ideal features to the extracted points from the real surface. In this paper an approach for automatic metrologi-cal inspection of manufactured parts is proposed. Starting from a tessellated model, coming from a scanned workpiece, the methodology carries out automatically the partition of the acquired surface by a shape recognition approach. Then, the ideal featu-res are associated to the corresponding non-ideal fea-tures, based on some criteria that permit to define the minimum zone solution. The proposed methodology stands out for the number and the types of the auto-matically recognized features. Finally, the form errors, related to all the recognized features, are eva-luated. In this paper the procedure has been used to eva-luate some specific form error typologies for several simulated case-studies and real objects. The results deriving from this experimentation are here critically discussed.