Design, Modelling and Characterisation of a Miniature Fibre-Reinforced Soft Bending Actuator for Endoluminal Interventions

Abstract

Miniaturised soft pneumatic actuators are crucial for robotic intervention within highly constrained anatomical pathways. This work presents the design and validation of a fibre-reinforced soft actuator at the centimetre scale for inte- gration into an endoluminal robotic platform for natural-orifice interventional and diagnostic applications. A single-chamber geometry reinforced with embedded Kevlar fibre was de- signed to maximise curvature while preserving sealing integrity, fabricated using a multi-stage multi-stiffness silicone casting process, and validated against a high-fidelity Abaqus FEM using experimentally parametrised hyperelastic material models and embedded beam reinforcement. The semi-cylindrical actuator has an outer diameter of 18,mm and a length of 37.5,mm. Single and double helix winding configurations, fibre pitch, and fibre density were investigated. The optimal 100 SH configuration achieved a bending angle of 202.9° experimentally and 297.6° in simulation, with structural robustness maintained up to 100,kPa and radial expansion effectively constrained by the fibre reinforcement. Workspace evaluation confirmed suitability for integration into the target device envelope, demonstrating that fibre-reinforcement strategies can be effectively translated to the centimetre regime while retaining actuator performance.

Figures (10)

• Figure 1: Cross-sectional dimensions and structure of the actuator. The green region denotes the cap, the yellow the Kevlar fibre winding, the thin grey sheet the inextensible fibreglass layer, the dark grey the air chamber, and the semi-transparent grey the silicone body. Symbols correspond to Table \ref{['tab:geomA-params']}. (a) Side view, (b) Front view, (c) Cross-sectional view.
• Figure 2: Fabrication of actuator with Geometry A: (a) Mould assembly for the inner chamber; Ecoflex 00–50 is injected to form the chamber wall. (b) A Kevlar fabric inextensible layer, pre-soaked in Ecoflex 00–50, is bonded to the flat surface of the half-cured inner chamber, and Kevlar fibre are wound through it. (c) The reinforced inner chamber is placed into the outer chamber mould, and Ecoflex 00–50 is injected. (d) Fully cured chamber structure incorporating inner chamber, inextensible layer, fibre reinforcement, and outer chamber. (e) Smooth-Sil 960 is poured into the cap mould, and the chamber structure is dipped to form the cap, with an air tube inserted. (f) Completed actuator with Geometry A.
• Figure 3: Illustration of the bending angle measurement method used in this study. Representative deformation of 30 DH actuator under FEM increasing internal pressure (0, 30, 60, 100 kPa).
• Figure 4: FEM simulation results for Geometry A actuator configurations. (a)–(e): SH fibre windings with turn counts of 9, 18, 30, 50, and 100, respectively. Pressures: (a) 62 kPa, (b) 93 kPa, (c)–(e) 100 kPa. (f)–(i): DH fibre windings at 100 kPa. (f) 30 turns with fibre radius halved (0.05 mm), modelled following modeling. (g) 30 turns, (h) 50 turns, (i) 100 turns DH. (j) DH actuator front view; (k) SH actuator front view.
• Figure 5: Comparison of average radial expansion for selected fibre winding configurations.