Print Email Facebook Twitter Adaptive deformable mirror dynamics and modular control Title Adaptive deformable mirror dynamics and modular control Author Ellenbroek, R.M.L. Contributor Verhaegen, M. (promotor) Faculty Mechanical, Maritime and Materials Engineering Department DCSC Date 2011-11-08 Abstract The refractive index of air varies a.o. with temperature, humidity, pressure and the CO2 concentration. Due to atmospheric turbulence this refractive index varies both in space and in time, leading to aberrations in images of light having passed though it. These aberrations limit the achievable resolution of optical telescopes such that the quality of their images is no longer diffraction limited. An adaptive optics (AO) system is a means to recover the diffraction limited quality of the images. This can be achieved a.o. by reflecting the incoming light on a deformable mirror (DM) that adapts its shape to the wavefront of this light such that some norm of the residual wavefront after reflection is minimal. In this thesis novel designs are considered for the DM and its control system. They are primarily aimed at the 8m class of telescopes in visible light, leading to a 200Hz controller bandwidth requirement and 6mm actuator spacing or 5000 actuators on a 500mm diameter DM.. To observe fainter celestial objects and/or increase the image resolution, optical telescopes are foreseen with primary mirrors of up to 40m in diameter. Therefore, the DM system design is aimed at extendibility to a larger number of Degrees Of Freedom (DOF), which is realized using a modular concept. Other drivers are low power consumption to prevent the need for active cooling systems and low production costs. The DM design is realized using electromagnetic reluctance type actuators that are connected to the DM's reflective membrane by a thin rod. Modules containing 61 hexagonally arranged actuators are manufactured using techniques suitable for mass-production. To generate the currents through the actuator coils, driver electronics are developed based on Pulse-Width Modulation (implemented in FPGAs) in combination with analog low-pass filters. Several prototype DMs are realized whose behavior is analyzed both statically and dynamically by comparing Wyko and laser vibrometer measurements with first principle models of the driver electronics, the actuators and the facesheet. To retain modularity of the system, a distributed control system architecture is foreseen in which each (group of) actuator(s) has its own controller that has a fixed computational power, communicates only to its neighbors and receives only a subset of the wavefront measurement data. The design of a distributed controller with good performance is complicated by the wavefront reconstruction step made necessary by the Shack-Hartmann wavefront sensor. Nevertheless, a distributed algorithm that combines wavefront reconstruction with adaptive prediction is shown in simulation to approximate the performance of a centralized finite impulse response (FIR) predictor/reconstructor and does not deteriorate as the number of DOFs increases. Subject adaptive opticsdistributed controldeformable mirrormodular designlow power To reference this document use: http://resolver.tudelft.nl/uuid:e7319b34-f901-4018-be78-797ab266599d Publisher Rogier Ellenbroek ISBN 9789090263632 Part of collection Institutional Repository Document type doctoral thesis Rights (c) 2011 Ellenbroek, R.M.L. Files PDF thesisrogier_websmall.pdf 6.7 MB Close viewer /islandora/object/uuid:e7319b34-f901-4018-be78-797ab266599d/datastream/OBJ/view