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The control system of adaptive optic of a large astronomical segmentated telescope was designed and tested. The dynamic model and the amplitude-frequency analysis of the new magnetic rheology (MR) drive are presented. The loop controlled drive consists of hydrostatic carrier, MR hydraulic loop controlling system, elastic thin wall seal, stainless seal which are united in a single three coordinate manipulator. This combination ensures short positioning error δφ⪅50 nm and small time of response. The main feature of a large astronomical telescope (diameter 25 m) is the large number (in our case 512) of primary mirror segments usage, which are united in one reflecting system. This design makes easier the problem of the primary mirror manufacturing but brings another problem to ensure precise movement of every mirror segment movement and to provides a perfect coincidence of the mirror segments constantly. Suggested parameters of the drive, based on magnetic rheology (MR) liquid are: precision δφ⪅50 nm, time of response T≤0.2 s. Error of positioning of loop-controlled MR drive may be expressed: δφ = δr + δdb + δf + δi, where δr -- 'reproduction' error (depends on drive structure and controlling system, and in our case the drive ensures δr = 0); δdb -- 'disturbance' error (δdb = 5...10 nm); δf -- error, because of static friction forces action (δf equals kt x Fst = 2 x Is/ki = 30 nm, where kt -- transformation coefficient of the drive; Fst -- static force in the drive; Is -- 'starting' current in the drive; ki -- transformation coefficient of the measuring system); δi -- 'instrumental' error. In case of a laser interferometer usage δi = 10 nm and the summarized error is δφ≤50 nm. Time of response T of the drive depends mainly on the combination of time constants of the next elements: MR-valve Tm, elastic elements (pipes, thin-wall tubes, bellows) Tel, moved object (mirror segments) Ts. Experiments show what the MR drive ensures: Tm = 20 ms, Tcl = 20 ms, Ts = 100 ms. Analysis of the amplitude-frequency graphs shows, that the MR-drive ensures summarized time of response till T≤110 ms.
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