DESIGN AND DEVELOPMENT OF A LONG-TRAVEL POSITIONING ACTUATOR AND TANDEM CONSTANT FORCE ACTUATOR SAFETY SYSTEM FOR THE HOBBY EBERLY TELESCOPE WIDE FIELD UPGRADE

The Wide Field Upgrade presents a five-fold increase in mass for the Hobby-Eberly Telescope’s tracker system. The design of the Hobby-Eberly Telescope places the Prime Focus Instrument Package (PFIP) at a thirty-five degree angle from horizontal. The PFIP and its associated hardware have historically been positioned along this uphill axis (referred to as the telescope’s Y-axis) by a single screw-type actuator. Several factors, including increased payload mass and design for minimal light obscuration, have led to the design of a new and novel configuration for the Y-axis screw-drive as part of the tracker system upgrade. Typical screw-drive designs in this load and travel class (approximately 50 kilonewtons traveling a distance of 4 meters) utilize a stationary screw with the payload translating with the moving nut component. The new configuration employs a stationary nut and translating roller screw affixed to the moving payload, resulting in a unique drive system design. Additionally, a second cable-actuated servo drive (adapted from a system currently in use on the Southern African Large Telescope) will operate in tandem with the screw-drive in order to significantly improve telescope safety through the presence of redundant load-bearing systems.

Details of the mechanical design, analysis, and topology of each servo drive system are presented in the paper, “Design and Development of a Long-Travel Positioning Actuator and Tandem Constant Force Actuator Safety

System for the Hobby Eberly Telescope Wide Field Upgrade,” coauthored by Nicholas Mollison, Jason Mock, Ian Soukup, Timothy Beets, Joseph Beno, Sarah Hinze, Douglas Wardell, and James Heisler (UTCEM) and John Good, Herman Kriel (UT McDonald Observatory) and presented at the SPIE Astronomical Telescopes and Instrumentation 2010, San Diego, California, 27 June-2 July 2010. The paper includes discussion of the issues such a configuration presents in the areas of controls, operational and failure modes, and positioning accuracy, and findings and results from investigations of alternative telescope safety systems, including deformable crash barriers

For more information please contact Dr. Joe Beno

Y-axis drivesystem layo9ut and major compontents. The full payload (hexapod, PFIP, WFC, etc.) and telescope upper hexagon structure are hidden from view to make interfaces within the tracker bridge and LHF more apparent.

 
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