Fig. 1. Block diagram of sliding mode control structure based on DOB

Fig. 2. Graph of the step signal response of c=4，k=3

Fig. 3. Graph of the sine response of c=4，k=3

Fig. 4. Graph of the step signal response of c=4，k=1

Fig. 5. Graph of the sine response of c=4，k=1

Fig. 6. Structure diagram of the tip-tilt mirror system

Fig. 7. Experimental device diagram

Fig. 8. Azimuth axis calibration curve of the tip-tilt mirror

Fig. 9. Pitch axis calibration curve of the tip-tilt mirror

Fig. 10. Azimuth axis correction error curve of the tip-tilt mirror

Fig. 11. Pitch axis correction error curve of the tip-tilt mirror