1,720,983 research outputs found
Automatic evaluation of form errors
No full textAutomating 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
Recognition of intrinsic quality properties for automatic geometric inspection
Full text linkIn 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
Automatic error evaluation of axial-symmetric surfaces
No full textThis paper aims at developing a suitable analysis of the point cloud, coming from the optic
scanning of a real object, allowing to evaluate automatically the errors without using a nominal
CAD model or a GPS specification. Really, this possibility is strictly depending on the capability
to recognize in a scanned tessellated model some intrinsic nominal references. This paper is
particularly devoted to the automatic error evaluation of axial – symmetric surfaces; for this kind
of surfaces two types of intrinsic references can be recognized. An original classification of the
error categories is proposed and the related methods for the evaluation of these errors are
presented. The methodology is applied to some real cases and the related results are critically
discussed
Fuzzy sets for geometric shape recognition in triangular meshes
Full text linkShape recognition of geometric models described
by triangular meshes is aected by some problems
which made it dicult to be performed without er-
rors. Some factors, such as the location errors of
points due to acquisition process and the coarse rep-
resentation of continuous surfaces due to triangular
approximation, introduce uncertainty in the recogni-
tion process of the geometric shape. This paper in-
troduces some original fuzzy sets suited to recognize
geometric form. The membership functions of the
fuzzy sets are dynamically dened so that they can
be adapted to take into account those properties of
the geometric model that aect the uncertainty of
the recognition process. The proposed approach is
intrinsically very robust and achieves good results
also in recognising form features in geometric mod-
els aected by point location errors
Fuzzy sets for geometric shape recognition in triangular meshes
No full textShape recognition of geometric models described by triangular meshes is affected by some problems which made it difficult
to be performed without errors. Some factors, such as the location errors of points due to acquisition process and the coarse
representation of continuous surfaces due to triangular approximation, introduce uncertainty in the recognition process of
the geometric shape. This paper introduces some original fuzzy sets suited to recognize geometric form. The membership
functions of the fuzzy sets are dynamically defined so that they can be adapted to take into account those properties of the
geometric model that affect the uncertainty of the recognition process. The proposed approach is intrinsically very robust
and achieves good results also in recognising form features in geometric models affected by point location errors
Confronto tra tecniche per il Riconoscimento di geometrie assialsimmetriche in modelli tessellati
No full textThe estimation of axis of axial symmetric geometries, and of other surface differential properties is essential for many applications of geometric models defined by triangular meshes. In this work two methods for axis determination, described in literature, are analyzed and compared. For each method several variants have been carried out; these variants differ for the evaluation criteria of some factors, such as the normal estimation at a vertex of the tessellated model. The methods are compared also in the analysis of models that differ each other for size and regularity of the mesh
Construction of a geometric reference model for automatic non ideality evaluation of an acquired high-density workpiece
Full text linkPurpose:
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
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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