Friction compensation strategies in large telescopes

David R. Smith; Kamal Souccar

doi:10.1117/12.857508

4 August 2010 Friction compensation strategies in large telescopes

David R. Smith, Kamal Souccar

Proceedings Volume 7733, Ground-based and Airborne Telescopes III; 77332N (2010) https://doi.org/10.1117/12.857508
Event: SPIE Astronomical Telescopes + Instrumentation, 2010, San Diego, California, United States

Abstract

For large telescopes, management of axis friction presents a significant challenge. In some cases, this is avoided or minimized in the design stage by employing hydrostatic bearings. However, the main axis servo systems of many large telescopes must cope with bearing or wheel friction. This friction affects or limits servo control performance in several ways. The most obvious is the stick-slip limit cycle that is characteristic of trying to hold position with an integrating control system in the presence of friction. If it is not taken into account, friction also introduces effects into the state estimation in model-based controllers. There are several standard approaches to friction compensation. These include dithering (introducing a noise signal to the drive motors), direct Coulomb friction compensation (sending an additional torque based on the rate command), and adaptive techniques based on monitoring of the final drive velocities. In this work, we experimentally compare different friction compensation approaches on the static positioning performance of the Large Millimeter Telescope/Gran Telescopio Milimetrico (LMT). Single and double integrator systems are investigated, as well as direct Coulomb friction compensation.

Citation Download Citation

David R. Smith and Kamal Souccar "Friction compensation strategies in large telescopes", Proc. SPIE 7733, Ground-based and Airborne Telescopes III, 77332N (4 August 2010); https://doi.org/10.1117/12.857508

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