Fig. 3

Mathematical model of the rod deformation and deformed-shape optimization. a We define the rod as linear and torsion springs for each interval separated by the disc. b The connection points of the tendon and segment are restrained with torsion springs of different strengths. c Mathematical model of the Penetration Model. The connection points of the tendon are constrained at the center of the segment. d The segments are parts of the rod between the discs. e The rod deforms like a bow for each segment, and the tendon’s linear springs are stretched to generate different tensions