AIMFAST for Heliostats: Canting Tool for Long Focal Lengths.

Accurate canting, or alignment, of heliostat facets is critical to the optical success of CSP tower systems. Canting accuracy for large fields must typically be on the order of 0.25mrad RMS. To date, heliostats are canted through dimensional control such as fixtures or touch probes, with potentially much higher error. AIMFAST (Alignment Implementation for Manufacturing using Fringe Analysis Slope Technique) is a fringe reflection (deflectometry) tool utilized to provide rapid, accurate optically-based canting of mirror facets on multi-facet CSP systems. AIMFAST was originally developed in support of 40-facet dish deployments by Stirling Energy systems in 2009 [1] and generalized to arbitrary dish systems in 2013 [2]. AIMFAST was demonstrated to meet alignment goals of <0.25 mrad RMS on dish systems, and accounts for structural deflections caused by gravity as the tracking structure rotates. This paper presents the extension of AIMFAST to large area heliostats. Multi-facet heliostats provide challenges to the fringe reflection method due to the nearly flat optical structure, leading to either multiple cameras or very large projection screens instead of LCD flat panels. Key elements include characterization of target image distortion from multiple projectors, boresighting of the subject heliostat, automated detection of errors, and automated adjustment tool interface. [ABSTRACT FROM AUTHOR]