Mechanical Surface Treatment to Obtain Optically Cooperative Surfaces vis-a-vis Fringe Projection

摘要

Fringe projection techniques are widely used for geometry measurement of synchro rings inside a manufacturing chain, since a dense areal geometrical data set is needed to evaluate all the key features. Post-process machined parts exhibit optically incooperative surfaces towards triangulation techniques. Hence these parts can't be measured accurately using fringe projection systems. The optical incooperativity originates from the scattering characteristics of the surface. Polished surfaces exhibit a narrow angle of light refraction, whereas rough surfaces scatter the light over a hemisphere more homogenously. The angle range at which an incident light ray is scattered is the basis for a definition of optical cooperativity. The wider the range, the higher is the optical cooperativity of the surface.rnIn order to produce optically cooperative surfaces of machined parts for the use of fringe projection measuring systems, we employ methods of surface treatment. One promising mechanical method under investigation to obtain optical cooperativity with technical surfaces is done by blasting the surface with fused alumina (EKF1000). The blasted surface leads to an increased roughness which can be controlled using the blast parameters, i.e. blast-pressure, blast-duration and the distance of the blaster to the part surface.rnIn this paper the effects of different parameters of the blast-process on the surface roughness, the optical roughness and on the optical cooperativity vis-a-vis fringe projection techniques are examined. Optimal parameter settings result in a sub-micrometer change with respect to the object surface. Since the effects due to a variation of the parameters are dependant on the object material, we restrict our research to the case-hardening steel 1.7193 (16MnCrS5).