Development of a laser-scattering-based probe for on-line measurement of surface roughness

The design and properties of an optical probe for on-line measurement of surface roughness are discussed. Based on light scattering, a probe that consists of a laser diode, a measuring lens, and a linear photodiode array was designed to detect surface roughness, in which the light scattered from a test surface at a relatively large scattering angle phi (=28 degrees) can be collected to enhance measuring range and repeatability. A coaxial design that incorporates a dual-laser probe and compressed air makes the proposed system insensitive to the position of the test surface and to surface conditions such as the presence of debris, vibration, and lubricants that result from machining. The results from measurements of several sets of specimens have demonstrated the feasibility of measuring surface roughness by using light scattering. On-line measurement on a diamond-turning lathe has shown that the proposed technique is stable and compact enough to be applicable to on-line measurement of surface roughness of an engineering surface.