Sep 15 2010
A giant telescope design is being developed by the European Southern Observatory and will in future revolutionise our understanding of the universe and its origins. Noliac bending actuator rings have the potential to provide solutions to control essential mirror deformations and are used in a UK Astronomy Technology Centre's (UKATC) proof of concept deformable mirror.
Giant telescopes
The design of the giant telescope comprises an array of almost 1000 mirrors to form a 42 metre diameter primary. It also includes adaptive optics as an integral part of the telescope, which will allow astronomers to correct the images for the twinkling caused by the turbulence of the Earth's atmosphere.
Noliac ring bender actuators in a test set up for a 300mm diameter deformable mirror. The initial tests were carried out using a 125mm glass mirror (2mm thick) and the plan is to introduce a 300mm compliant carbon silicon carbide (C/SiC).
The deformable mirror design takes advantage of the fast, milli-second, response time of piezo in correcting for atmospheric distortions and can accurately manipulate the mirror surface to sub micron resolution. The exceptional displacement range of the ring bending actuator enables tens of microns of displacement, sufficient to have a considerable impact on reducing other residual errors relating to the telescope error budget.
A matrix consisting of ring bending actuators, on a 30mm pitch, are bonded to the underside of the mirror and provide a compact assembly. The multi-layer design of the actuator enables the required distortive force to be achieved at a sufficiently low voltage that the drive electronics design is simplified, and the bias voltage applied to the actuator considerably simplifies the mechanical design of the support. The design has provision for displacement sensing which will be used to reduce the hysteresis of the system to below 1% (piezo actuators typically have a 10% hysteresis).