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Abstract

A surface roughness measuring apparatus (11) has a probe (27, 41) with a smooth surface region (31, 43) contoured to conform to a surface (33) the roughness of which is to be measured, and an aperture (25, 49) located generally centrally of the smooth surface region of the probe. Illustratively, the workpiece surface is a generally flat annular surface portion of a disk brake rotor (35). The test probe surface is juxtaposed with the workpiece surface and a fluid pressure modifying mechanism such as an air vacuum pump (15) and driving motor (17), which are coupled to the probe aperture, are energized to induce a fluid pressure differential between the aperture and peripheral portions of the surface region. A fluid parameter monitoring device such as air flow meter (23) or air pressure meter (19) measures a fluid response to the induced fluid pressure differential and the roughness is inferred from the measured fluid behavior. A valve (21) for selectively blocking fluid flow between the aperture (25) and the vacuum pump (15) allows the fluid pressure measuring device (19) to determine the rate of change of the induced fluid pressure differential, or a measure of the fluid flow may be utilized to infer the roughness of the workpiece surface. A similar fluid behavior technique may be employed using the probe on a sample of known surface roughness to calibrate the system.

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