Profile Tolerance Verification for Free-form Surfaces Using Medial Axis Transform

• Published in: Procedia CIRP 2013, Vol.10, p.133-141
• Main Authors: Kale, Kishor B., Gurumoorthy, B.
• Format: Article
• Language: English
• Subjects: Free-form surface; Medial Axis Transform; Profile Tolerance
• ISSN: 2212-8271; 2212-8271
• DOI: 10.1016/j.procir.2013.08.023

Tolerances for freeform surfaces are specified using profile tolerance that controls form or combination of size, form, orientation and location of a feature(s) relative to a true profile. Freeform surfaces are generally inspected by using fixtures on a coordinate measuring machine (CMM). The combination of fixtures and the CMM enables the establishment of correspondence between points on the machined and nominal surface for tolerance verification. To respond to the market quickly, it has become inevitable to use 3D scanners that can scan an object rapidly and provide dense unorganized points as an output without maintaining any correspondence with the nominal CAD model. Current state of art uses the shortest distance criterion to establish correspondence and verify the profile tolerances. This results in acceptance of parts that ought to be rejected and vice versa. A novel, alternative approach is proposed to overcome this deficiency and verify tolerances specified on a free-form surface. The technique establishes the correct one to one correspondence between the machined surface and CAD model using the Medial axis transform (MAT). The MAT of both the nominal surface and the measured points respectively, are discretised to obtain grids. Corresponding points on the two grids are then used to verify the deviation of the machined surface from the nominal surface. Results of preliminary experiments with simulated data are presented.