Fig. 1. FBG silicone rubber sensing unit

Fig. 2. Schematic of sliding mechanism

Fig. 3. Optical transport characteristics of the FBG

Fig. 4. Profile strain analysis

Fig. 5. Slider and surface material

Fig. 6. Three materials versus center wavelength

Fig. 7. Schematic of feature mapping process

Fig. 8. Confusion matrix

Fig. 9. Three-dimensional characteristic values of each material

Fig. 10. Number of iterations versus minimum classification error

Fig. 11. Material recognition step-by-step

Fig. 12. Photo of the system hardware

Fig. 13. Host computer interface