22 July 2010 Fast force actuators for LSST primary/tertiary mirror
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Abstract
The very short slew times and resulting high inertial loads imposed upon the Large Synoptic Survey Telescope (LSST) create new challenges to the primary mirror support actuators. Traditionally large borosilicate mirrors are supported by pneumatic systems, which is also the case for the LSST. These force based actuators bear the weight of the mirror and provide active figure correction, but do not define the mirror position. A set of six locating actuators (hardpoints) arranged in a hexapod fashion serve to locate the mirror. The stringent dynamic requirements demand that the force actuators must be able to counteract in real time for dynamic forces on the hardpoints during slewing to prevent excessive hardpoint loads. The support actuators must also maintain the prescribed forces accurately during tracking to maintain acceptable mirror figure. To meet these requirements, candidate pneumatic cylinders incorporating force feedback control and high speed servo valves are being tested using custom instrumentation with automatic data recording. Comparative charts are produced showing details of friction, hysteresis cycles, operating bandwidth, and temperature dependency. Extremely low power actuator controllers are being developed to avoid heat dissipation in critical portions of the mirror and also to allow for increased control capabilities at the actuator level, thus improving safety, performance, and the flexibility of the support system.
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Edward Hileman, Edward Hileman, Michael Warner, Michael Warner, Oliver Wiecha, Oliver Wiecha, } "Fast force actuators for LSST primary/tertiary mirror", Proc. SPIE 7739, Modern Technologies in Space- and Ground-based Telescopes and Instrumentation, 773936 (22 July 2010); doi: 10.1117/12.857785; https://doi.org/10.1117/12.857785
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