Fig. 7: Black box exploration of the SMF: Step 2 and Step 3.

Step 2: a The SMF probed the four regions R1 to R4 from a reference level at a compression speed of 10 mm s⁻¹, and the collected Ch1 signals are shown in (b). c Result of Step 2 shows that R1 is a pit, R2 and R3 have raised obstacles, and R4 is a plane. Step 3: Object types of the obstacles were judged. d Ch1 signals were obtained by pressing R2 and R3 with a compression speed of 10 mm s⁻¹ and a displacement of 3.5 mm for three times and inputted to the LightGBM classifier for prediction. e Prediction result indicates that R2 is made of porous plastics and R3 is made of cured resin. f Result of Step 2 and Step 3, which is consistent with the actual situation.