Air test to determine surface roughness
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.
1. A process of inferring a measure of the roughness of a workpiece surface, comprising the steps of:
juxtaposing a surface on a probe and the workpiece surface;
impressing a fluid pressure differential between peripheral portions of an interface between the test probe surface, the workpiece surface and a central region of the probe;
measuring a fluid response to the impressed fluid pressure differential while maintaining the pressure differential at a preferred level;
terminating the impressing of the fluid pressure differential;
measuring the time rate of change of said pressure differential after said termination; and
inferring a measure of the roughness of the workpiece surface from the measured fluid response.
2. The process of claim 1 , wherein the step of juxtaposing includes urging the workpiece and probe surfaces into engagement with a predetermined force.
3. The process of claim 1 , wherein the fluid comprises ambient air.
4. The process of claim 1 , including the preliminary step of contouring a foot of the probe to have a surface shape highly similar to the shape of the workpiece surface.
5. The process of claim 1 , including the additional steps of:
engaging the foot of the test probe with a sample surface;
establishing an air pressure differential by air flowing across the junction between the sample surface and test probe foot;
measuring a resulting pressure differential caused by said air flow along the junction between the sample surface and test probe foot; and
comparing the measured air flow along the junction between the sample surface and test probe foot with the measured air flow along the junction between the workpiece surface and test probe foot.
6. The process of claim 1 , wherein the air pressure differential established between the sample surface and test probe foot is substantially the same as the air pressure differential established between the workpiece surface and test probe foot.
7. The process of claim 1 , wherein the step of engaging the foot of the test probe with a sample surface includes clamping the foot to the sample surface with a predetermined force, and the step of engaging a foot of a test probe with the workpiece surface includes clamping the foot to the workpiece surface with substantially the same predetermined force.