Non-contact profilometry of E-ELT segments at OpTIC Glyndwr

Carolyn Atkins; John Mitchell; Paul Rees

doi:10.1117/12.893690

27 September 2011 Non-contact profilometry of E-ELT segments at OpTIC Glyndwr

Carolyn Atkins, John Mitchell, Paul Rees

Author Affiliations +

Proceedings Volume 8126, Optical Manufacturing and Testing IX; 81260M (2011) https://doi.org/10.1117/12.893690
Event: SPIE Optical Engineering + Applications, 2011, San Diego, California, United States

Abstract

Following a 'Call for Tenders' by the European Southern Observatory (ESO) a collaboration headed by OpTIC Glyndwr Ltd is producing seven prototype segments for the European Extremely Large Telescope (E-ELT). Each hexagonal segment is 1.4 m corner-to-corner with a base radius of curvature (ROC) of 84 m and the combination of 984 segments will lead to a primary mirror with a diameter of 42 m. The polishing of the prototype segments occurs in-house at OpTIC Glyndwr using a Zeeko polishing machine, while in situ interferometry is undertaken using a specifically designed optical test tower built above the polishing machine. To confirm the base radius of curvature of the prototype segments an on-machine non-contact profiler is used. The profiler attaches to the bridge of the polishing machine and is removed during polishing. The design of the profiler is based upon a nanometre optical component measuring machine (NOM) system, originating from the sychrotron optics community. This instrument determines the height at a series of points across the surface through the integration of measured slope data. This paper presents the operation of the OpTIC-NOM as both an on-machine and off-machine profiler. The accuracy of the profiler both on- and off-machine and its accuracy is compared against similar profilers through its participation in a round robin study. Radius of curvature results are presented for the master spherical segment (MSS), which is a reference optic for the E-ELT segments and highlights a standard deviation on the mean radius of curvature of 2.5 mm. Finally, a summary of future work is presented regarding the polishing of the prototype segments and the development of a stitching algorithm to produce 3D surface maps from profilometry data.

Citation Download Citation

Carolyn Atkins, John Mitchell, and Paul Rees "Non-contact profilometry of E-ELT segments at OpTIC Glyndwr", Proc. SPIE 8126, Optical Manufacturing and Testing IX, 81260M (27 September 2011); https://doi.org/10.1117/12.893690

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