Fig. 1. Sensing model of a soft mainpulator based on helical FBG

Fig. 2. (a) Side view; (b) Enlarged view of terminal structure; (c) Cross sectional view

Fig. 3. (a) Soft manipulator embedded with FBG-based optical fiber in a helical configuration; (b) Top view of the connecting surface; (c) Enlarged state of the FBG-based optical fiber

Fig. 4. Moulding process of the soft manipulator with helically embedded FBGs-based optical fibre sensor. (a) Helical groove moulding step of the manipulator base with helical groove; (b) Optical fibre is wound along the helical groove of the manipulator; (c) The manipulator is encapsulated in a layer of silicone to anchor the optical fibre; (d) Kevlar fiber is wound along the manipulator; (e) All mould are removed and one end of the manipulator is capped

Fig. 5. Experimental setup of for measuring compression and bending movements. (a) Optical fiber sensing system; (b) Soft manipulator and its pneumatic driving control system, etc

Fig. 6. Snapshots of soft manipulator with different bending angles

Fig. 7. Relationship between input pressure and bending angle of soft manipulator

Fig. 8. Wavelength shift of 3 FBGs with different bending states

Fig. 9. Relationship of wavelength shift and bending angle

Fig. 10. Stability results of the helically embedded FBGs-based optical fiber sensor