IMProVe 2011 - Proceedings

Geometric Product Specification and Tolerancing
Form errors estimation in free-form 2D and 3D geometries
A. Cerardi (a), R. Meneghello (a), G. Concheri (a), G. Savio (a)
(a) Università di Padova
Abstract:
Purpose:
The aim of this work is to present a method for the verification of form tolerances in freeform
geometries.
Method:
New free-form error parameters, in accordance with ISO GPS standards are defined.
Geometrical errors in 2D e 3D geometries are calculated using a new fitting method
consisting in an association operation where nominal profile/surface is resized (with an
offset), located and oriented on the non-ideal geometry. Form tolerance is estimated
using peak-to-valley deviation after the best fit.
Result:
Automatic algorithms are implemented to analyse 2D free-form profiles of moulds for
ophthalmic lenses obtained with grinding and polishing operations and to analyse 3D freeform
surfaces of an injection moulded lamp lens for automotive industry.
Discussion & Conclusion:
The comparison between results obtained using this approach and using traditional fitting
methods shows differences on the fitting and errors parameters estimation. In particular
in the traditional fitting there is a repartition of the size error contribution in the
translation and form errors. The differences increase proportionally to the offset value
estimated. The calculation of offset parameter allows the separation of size from
geometric errors in free-form profiles/surfaces and the “true” form error estimation.
Keywords: Geometric Product Specification, Free-form inspection, Profile tolerancing,
Product verification, Verification method
Corresponding Author: Andrea Cerardi
Tel.: +39 049 8276734
Fax.: +39 049 8276738
e-mail: andrea.cerardi@unipd.it
Address: via Venezia, 1, 35131 Padova Italy.
June 15 th – 17 th , 2011, Venice, Italy
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IMProVe 2011 - Proceedings