Fig. 1. System schematic

Fig. 2. Traditional two-stage control system

Fig. 3. Improved two-stage control system

Fig. 4. Closed loop system of the coarse stage

Fig. 5. Frequency response curve of the Stewart platform

Fig. 6. Closed loop system of the fine stage

Fig. 7. Integral controller and pi-pi control error suppression curve simulation diagram

Fig. 8. Experimental diagram of the two-stage system

Fig. 9. The error suppression curve of the PI and PI-PI controller is compared

Fig. 10. The two-stage system experiment. (a) f=0.05 Hz; (b) f=0.80 Hz

Fig. 11. The process of unloading quantization in two-stage control

Fig. 12. The tracking error of single-order structure and two-step structure is compared. (a) 0.01 Hz；(b) 0.02 Hz；(c) 0.05 Hz