Fig. 1. Structure of the orbital crawling hole-making robot

Fig. 2. Flow chart of measuring reference hole

Fig. 3. Comparison of reference holes. (a) Ordinary reference hole; (b) reference hole with core clip

Fig. 4. Gray distribution of the reference hole image with the core clip

Fig. 5. Searching process of the concave point

Fig. 6. Rough positioning of the reference hole profile. (a) Pole and pole chord theorem of the ellipse; (b) rough positioning of the actual reference hole

Fig. 7. Schematic diagram of the profile fitting

Fig. 8. Schematic diagram of the hand-eye calibration. (a) Hand-eye calibration coordinate system; (b) schematic diagram of the special target

Fig. 9. Diagram of the experimental setup. (a) Hole-making robot; (b) position of the vision system

Fig. 10. Reference hole positioning results under different parameters. (a) δ_dis=3; (b) δ_dis=6; (c) δ_dis=10

Fig. 11. Positioning results of our method under different lighting conditions. (a) Light is weak; (b) light is moderate; (c) light is strong

Fig. 12. Positioning results of different contours. (a) Small part of the reference hole edge; (b) most of the reference hole edge; (c) all the reference hole edges