Non-contact surface roughness measurement of round bars considering the effect of machining striations

By measuring scattered light, our goal is to improve the accuracy and automation of manual inspection. In this study, we attempted to measure the non-contact surface roughness of the curvature surface of a round bar sample by capturing and analyzing the scattered light distribution. We also evaluated the influence of machining marks on the round bar. A round bar workpiece (cold forged material, surface polished) was irradiated with a He-Ne laser (spot diameter Φ0.8 mm, maximum power 8 mW, wavelength 632.8 nm) and a PIN photodiode (sensor size Φ1.5 mm) was scanned to acquire the scattered light intensity distribution. The detected scattered light distribution was fitted to a scattered light distribution model based on the generalized Harvey-Shack theory to calculate surface roughness parameters. The extracted roughness parameters are root mean square roughness ”Rq” and half width of autocovariance ”lc”. The PIN photodiode was scanned in the direction of the machining striations and in the direction orthogonal to the striations, and the ratio of the lc in the two directions was used to evaluate the surface roughness anisotropy parameter ”Str”. By determining ”Str”, we can consider the effect of machining striations on machine performance. This paper presents the results of the evaluation of Str compared to the conventional method, which allows non-contact, non-destructive measurement.