We describe a visual method for aligning physically separated, large structures using a Bessel beam to define a common datum. The equipment consists of an alignment telescope, used to generate and project the optical beam, and a series of crosswire targets fitted to each structure. Alignment is achieved by eye using a loupe or CCD camera to observe superposition of the Bessel intensity structure and crosswire shadow. The method is simple and intuitive, and can be implemented on a low budget. The combination of structured beam profile and low beam divergence allows a best-case alignment accuracy of 10 microns under lab conditions for beam lengths of 19 metres, decreasing to 30-50 microns r.m.s. for field measurements. The self-regeneration property of the Bessel beam facilitates the location of multiple beam targets with negligible degradation in beam quality. Error sources include Bessel ring - target wire mismatch, target centering/ roundness errors, and air turbulence.

Date Published: 27 May 2011
PDF: 12 pages
Proc. SPIE 8082, Optical Measurement Systems for Industrial Inspection VII, 80823D (27 May 2011); doi: 10.1117/12.889300

Published in SPIE Proceedings Vol. 8082:
Optical Measurement Systems for Industrial Inspection VII
Peter H. Lehmann; Wolfgang Osten; Kay Gastinger, Editor(s)