Precise Alignment of Workpieces Using Speckle Patterns as Optical Fingerprints

Engineering process chains sometimes require a precise repositioning method of workpieces within production machines and measuring devices. This causes difficulties, however, if the workpiece may not be marked permanently in order to set up a sample coordinate system. This paper presents a repositioning method based on the unique statistical properties of monochromatic speckle patterns emerging from a specific spot of a rough workpiece surface. The speckle pattern could be regarded as an individual “fingerprint” of this specific surface spot. The influence of the experimental parameters (laser wavelength, beam diameter, wavefront curvature) on the uncertainty of relocation is discussed.