Automatic evaluation of form errors in high-density acquired surfaces

Abstract

International audienceIn this paper the authors present an original methodology aiming at the automation of the geometric inspection, starting from a high-density acquired surface. The concept of intrinsic nominal reference is herein introduced in order to evaluate geometric errors. Starting from these concepts, a new specification language, which is based on recognizable geometric entities, is defined. This work also proposes some surface differential properties, such as the intrinsic nominal references, from which new categories of form errors can be introduced. Well-defined rules are then necessary for the unambiguous identification of these intrinsic nominal references. These rules are an integral part of the tolerance specification. This new approach requires that a recognition process be performed on the acquired model so as to automatically identify the already-mentioned intrinsic nominal references. The assessable errors refer to recognizable geometric entities and their evaluation leaves the nominal reference specification aside since they can be intrinsically associated with a recognized geometric shape. Tolerance specification is defined based on the error categories which can be automatically evaluated and which are an integral part of the specification language

Shrinkage-based die design for drying ceramic parts

“…An error map is a colour-coded representation of normal deviation of each point in a cloud from the ideal surface. 16 What naturally precedes the extraction of the error map is the process of surface registration. As a general rule the coordinate system of the coordinate measuring machine used in the dimensional inspection of a complex part is different from the coordinate system of the CAD model, against which the comparison takes place.…”

An investigation on methods for axis detection of high-density generic axially symmetric mechanical surfaces for automatic geometric inspection

“…Thanks to these methodologies, the geometric verification can be performed automatically without the need for a CAD model, neither for partitioning the discrete model nor as reference for the error evaluation. 3 An overview of these methodologies has been recently proposed in Guardiani and Morabito. 4…”

“…High-density digitalization of surfaces is opening up new opportunities, such as: – The definition of novel geometric properties to inspect , such as the new form errors proposed to verify characteristics not yet considered by current GPS standards. 2,3 – The development of new procedures for a more robust verification process of traditional tolerances , such as the evaluation of the generatrix straightness error. 2,3 – The definition of automatic methodologies for the segmentation of discrete geometric models able to differentiate the surface features for functional importance .…”

“…2,3 – The development of new procedures for a more robust verification process of traditional tolerances , such as the evaluation of the generatrix straightness error. 2,3 – The definition of automatic methodologies for the segmentation of discrete geometric models able to differentiate the surface features for functional importance . In this respect, a methodology based on fuzzy logic has been recently proposed for distinguishing primary features from the secondary ones (such as fillets, rounds and grooves), in agreement with what is done in the engineering practice.…”

“…– The definition of novel geometric properties to inspect , such as the new form errors proposed to verify characteristics not yet considered by current GPS standards. 2,3…”