Non-contact, in-line inspection of surface finish of crankshaft journals

Crankshaft bearings of an automotive engine require smooth and high reliability performance as they operate in a harsh environment of heat, pressure, abrasion, and chemical attack that may cause wear. The bearings are designed to meet high precision tolerances and require high-quality surface finish and surface topography. The journals are first grounded and finally polished to an outstanding surface finish in the order of sub-micrometers. In a mass production process, the tapes that are used for final polish may break without being revealed by the automation. Therefore, it is essential to provide an in-line inspection system for such parts to eliminate manual inspection. In order to achieve this goal, we developed a machine vision technique to validate that all journals were polished and detect the unpolished ones. In utilizing this technique, a full-size prototype go/no-go demonstrator was built to validate the performance and reliability of the method. The sensitivity of the system is high enough to differentiate sub-micron level roughness change of the crankshaft surface.