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27 July 2016 Characterization of friction in the 3.6m Devasthal optical telescope
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In this paper, we present the work on characterization of friction in the 3.6 m Devasthal optical telescope axes. The telescope azimuth axis is supported on a hydrostatic bearing while the altitude and rotator axes are supported on hydrodynamic bearings. Both altitude and azimuth axes are driven directly by high power BLDC motors and the rotator is driven by BLDC motor via a gearbox. This system is designed by AMOS, Belgium and tuned to achieve a tracking accuracy better than 0.1 arcsec RMS. Friction poses control related problems at such low speeds hence it is important to periodically characterize the behaviour at each axes. Compensation is necessary if the friction behaviour changes over the time and starts dominating the overall system response. For identifying friction each axis of telescope is rotated at different constant speeds and speed versus torque maps are generated. The LuGre model for friction is employed and nonlinear optimization is performed to identify the four static parameters of friction. The behaviour of friction for each axis is presented and the results are discussed.
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T. S. Kumar, Christian Bastin, and Brijesh Kumar "Characterization of friction in the 3.6m Devasthal optical telescope", Proc. SPIE 9906, Ground-based and Airborne Telescopes VI, 99063X (27 July 2016);


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