Fig. 1. Variable aperture driven by ultrasonic motor

Fig. 2. Stator and rotor normal contact model

Fig. 3. Relationship between the tangential force and the speed of the rotor

Fig. 4. Experimental principle

Fig. 5. Image recognition

Fig. 6. Input and output curves

Fig. 7. Gray box model and error when the aperture is opened

Fig. 8. Gray box model and error when the aperture is closed

Fig. 9. Gray box model correlation diagram when opened

Fig. 10. Gray box model correlation plot when closed

Fig. 11. Error when the aperture is opened

Fig. 12. Error when the aperture is closed