Fig. 1. Block diagram of open loop frequency identification

Fig. 2. Frequency response of speed open-loop for elevation axis

Fig. 3. Frequency response of speed open-loop for elevation axis with and without structural filter

Fig. 4. Principle diagram of LADRC for velocity loop

Fig. 5. Principle diagram of control for position loop

Fig. 6. Experimental servo platform of 2.5 m telescope

Fig. 7. Bode diagram of velocity closed loop with and without structural filter

Fig. 8. Bode diagram of position closed loop

Fig. 9. Position and velocity response of 1.24° step with TD

Fig. 10. Position and velocity response of 1.24° step without TD

Fig. 11. Position and velocity response of 60° step with TD

Fig. 12. Position and velocity response of 60° step without TD

Fig. 13. Position response for sine command with LADRC

Fig. 14. Position response for sine command with PI control

Fig. 15. Position response for slope command with LADRC

Fig. 16. Position response for slope command with PI control

Fig. 17. Comparison of 0.01 （°）/s step response when loaded at 0.5 s and unloaded at 1.5 s

Fig. 18. Load torque estimated by LESO when loaded at 0.5 s and unloaded at 1.5 s