B6.2 - High Precision Multi Dimensional Displacement Sensors for Segmented Mirror Telescopes

SENSOR+TEST Conferences 2011
2011-06-07 - 2011-06-09
Proceedings SENSOR 2011
B6 - Dimensional Measurement
R. Hoenicka, M. Wasmeier - MICRO-EPSILON Messtechnik GmbH & Co. KG, Ortenburg (Germany)
315 - 318


New optical-infrared telescopes like the E-ELT (European Extremely Large Telescope) require the application of displacement sensors with enhanced specifications. The main mirrors of such big telescopes are designed from more hexagonal mirror segments. To adjust the whole mirror, all adjanced segments have to be adjusted multi dimensional. Therefore, on every edge on the back of the segments, so called edge sensors are mounted.
With the experience from LAMOST (Large Sky Area Multi-Object Fiber Spectroscopic Telescope), Micro-Epsilon has developed such a multi dimensional displacement sensor on the basis of an eddy current sensor. The system exists of a drive and a sense unit, positioned on every edge between two adjacent segments. The alignment in an unconditioned environment was in addition to a low nanometer resolution in at least one of 3 dimensions a main challenge. To reach the specification an improvement of all individual parts and the integration had to be done. Parts of this were the thermal simulation of the mechanics with an optimization of the used materials and the field simulation in addition with tests of different sensor geometry. Because of the required long term stability from the whole sensor system, in addition to the mechanics and the electronic parts with low temperature coefficient a new technology from Micro Epsilon, called embedded coil technology (ECT), is used instead of conventionally wounded coils.

Other difficult aspects are the alignment of the sensor units and the cross talk, which means the interference between two sensor units. To allow the changeability of the sensor units the mechanics is designed from 3 single parts on the drive and the sense unit. Thesingle parts can be aligned separately to adjust tolerances from the segments or the electronic parts. First measuring results from environmental and dynamic tests show the feasibility of the sensor concept.