Enclosure rotation on the Large Binocular Telescope

摘要

After several years of operation the enclosure rotation system of the LBT is exhibiting wear and other performanceissues that may impact operations. This paper reviews the system design and assumptions used, describes the currentperformance and observed symptoms, and discusses recent improvements made to improve performance and reliability.The rotating enclosure of the LBT is a 2200 ton structure riding on four bogies with a total of 20 wheels. Identifieddeficiencies include wheel bearing capacities, bogie misalignment, and rail loading. These are partially due to excessenclosure weight, which was supposed to be 1600 tons, but also due to design errors.The most serious problem was the failure of several wheel bearings. The bearings were not designed for fieldserviceability, so a crash program began to determine how to replace them. This got us back on sky quickly, but areview of the engineering calculations identified an error which led to the use of undersized bearings. A method ofinstalling a larger bearing was found, and these have been installed.One set of bogie wheels are misaligned so severely the structure makes loud popping and banging noises when thedirection of building rotation changes. The bogie needs to be rotated about its vertical axis, but there was no provision inthe design for this.The circular rail the bogies roll on is wearing faster than expected. The rails are extremely difficult to replace, so theshort term plan is to study the problem.© (2012) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.