High accuracy error separation technique for on-machine measuring straightness

A novel time-domain method, which can reconstruct straightness profile of workpiece exactly for on-machine measurement, has successfully been developed. The proposed method is based on difference measurement and can use two or three displacement probes. It possesses the following characteristics: (i) adapting to long or short workpiece, (ii) assuming no prior knowledge, (iii) employing large shears, (iv) needing no accurate zero-adjustment of probes, and (v) reconstructing various surfaces including smooth, non-smooth, periodic, and non-periodic profile with no theoretical error. The theoretical analysis and simulation justify the effectiveness of this method. Finally, the measurement system consisting of an autocollimator and two non-contact capacitive probes is built and evaluated experimentally on a diamond turning machine. This system can remove both pitching and translational error motion of the scanning stage.