Motion control design of the SDSS 2.5 mts telescope

This paper describes the control system analysis and design for the three principal axes of the 2.5 mts SDSS Telescope. The telescope requirements are good tracking performance with errors lower than 165 marcsec rms in the speed range between 0 to 45 arcsec/sec for all the axes. The pointing error is about 2 arcsec rms per axis with a maximum absolute value of 5 arcsec. The telescope has the additional requirement of slewing, between tracking areas, with maximum speed of 3 degree/sec. The dynamical model of the telescope including the friction is analyzed and based on that, the design of a PID controller for each axis is presented. The specifications for pointing and tracking mode are achieved with this design in all the range of velocities and the performance in slew-mode is acceptable. Simulations and experimental results depict the behavior of the telescope in slewing, tracking and pointing.