Development of a novel actuator concept for position control of segmented mirrors of ELT

Abstract

ABSTRACT Currently, a number of astrophysical institutes all over the world are working on the design of Extremely Large Telescopes (ELT). Due to the enormous size of the primary mirror these telescopes make use of segmented mirrors. These segments have to be positioned with respect to each othe r with nanometer accuracy in sp ite of all kind of external disturbances such as wind loads, therma l loads, deformation of the base frame, varying orientation with respect to the field of gravity, etc. Janssen Precision Engineering (JPE) developed a revolutionary position actuator called the HiPAC which is able to fulfill the demanding requirements for this kind of actuators. The actuator is based on an integrated system of a pneumatic actuator, an el ectric voice coil and smart control strategy and has the following features: x high positioning accuracy performance due to play-free and frictionless actuation; x high reliability and maintenance free operatio n due to flexure-based frictionless guiding; x system behavior is constant in time, because no parts affected by wear are used in the actuator; x low cost, because no highly accu rate machined parts required to reach high end performance; x the position actuator acts as an integrated vibration isolator which isolates the segmented mirrors from external vibrations induced in the telescope frame; In this paper the design, simulation and measurements of the HiPAC actuator will be presented. Keywords: Positioning actuator, mirror support, control strategy , sky-hook control, segmented mirror, ELT, HiPAC