Nanometre-accurate form measurement machine for E-ELT M1 segments

A. Bos, R. Henselmans, P.C.J.N. Rosielle, M. Steinbuch

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To enable important scientific discoveries, ESO has defined a new ground-based telescope: the European Extremely Large Telescope (E-ELT). The baseline design features a telescope with a 39-m-class primary mirror (M1), making it the largest and most powerful telescope in the world. The M1 consists of 798 hexagonal segments, each about 1.4 m wide, but only 50 mm thick. In the last stages of the manufacturing process of these M1 segments, a nanometre-accurate metrology method is required for the M1 to be within specifications. The segments have to be measured on their whiffle-tree support structures with a nanometre-level uncertainty, with a total budget on form accuracy of 50 nm RMS for any segment assembly. In this paper a measurement machine design is presented based on a non-contact single-point scanning technique, capable of measuring with nanometre accuracy, being universal, fast and with low operational costs, providing suitable metrology for M1 segments. A tactile precision probe is implemented to be able to use the machine in earlier stages of the segment manufacturing process. In particular, this paper describes the design of the air-bearing motion system and the separate metrology system based on a moving Sintered Silicon Carbide tube, a fixed Zerodur metrology frame and an interferometric system for a direct and short metrology loop. Preliminary calculations show nanometre-level measurement uncertainty after calibration.

Originele taal-2Engels
Pagina's (van-tot)14-25
Aantal pagina's12
TijdschriftPrecision Engineering
Volume40
DOI's
StatusGepubliceerd - 1 apr 2015

Vingerafdruk

Telescopes
Bearings (structural)
Sintered carbides
Level measurement
Machine design
Antenna grounds
Silicon carbide
Mirrors
Calibration
Scanning
Specifications
Air
Costs
Uncertainty

Citeer dit

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abstract = "To enable important scientific discoveries, ESO has defined a new ground-based telescope: the European Extremely Large Telescope (E-ELT). The baseline design features a telescope with a 39-m-class primary mirror (M1), making it the largest and most powerful telescope in the world. The M1 consists of 798 hexagonal segments, each about 1.4 m wide, but only 50 mm thick. In the last stages of the manufacturing process of these M1 segments, a nanometre-accurate metrology method is required for the M1 to be within specifications. The segments have to be measured on their whiffle-tree support structures with a nanometre-level uncertainty, with a total budget on form accuracy of 50 nm RMS for any segment assembly. In this paper a measurement machine design is presented based on a non-contact single-point scanning technique, capable of measuring with nanometre accuracy, being universal, fast and with low operational costs, providing suitable metrology for M1 segments. A tactile precision probe is implemented to be able to use the machine in earlier stages of the segment manufacturing process. In particular, this paper describes the design of the air-bearing motion system and the separate metrology system based on a moving Sintered Silicon Carbide tube, a fixed Zerodur metrology frame and an interferometric system for a direct and short metrology loop. Preliminary calculations show nanometre-level measurement uncertainty after calibration.",
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Nanometre-accurate form measurement machine for E-ELT M1 segments. / Bos, A.; Henselmans, R.; Rosielle, P.C.J.N.; Steinbuch, M.

In: Precision Engineering, Vol. 40, 01.04.2015, blz. 14-25.

Onderzoeksoutput: Bijdrage aan tijdschriftTijdschriftartikelAcademicpeer review

TY - JOUR

T1 - Nanometre-accurate form measurement machine for E-ELT M1 segments

AU - Bos, A.

AU - Henselmans, R.

AU - Rosielle, P.C.J.N.

AU - Steinbuch, M.

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KW - European

KW - Extremely

KW - Giant telescopes

KW - Ground-based astronomy

KW - Large Telescope (E-ELT)

KW - Measurement machine

KW - NANOMEFOS

KW - Non-contact

KW - Segment metrology

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JO - Precision Engineering

JF - Precision Engineering

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