Dynamics of Hybrid-Actuated Soft Robots with Stiffness Adaptation for Robot-Assisted Interventions

The lack of adaptability in surgical instruments has limited the widespread adoption of robot-assisted interventions. The objective of this doctoral research was to address the inherent trade-off between the deformability and force transmission capacity of minimally invasive surgery (MIS) instruments. Current instruments, such as catheters, tend to exhibit either excessive flexibility, rendering them unsuitable for load-bearing tasks, or excessive stiffness, limiting maneuverability in anatomical regions with complex geometry. The hypothesis underlying this research proposed that by controlling the stiffness of a soft robot, which serves as an MIS instrument, it is possible to increase its deformability during the steering phase while increasing stiffness during load-bearing tasks to ensure effective force transmission. The approach put forth in this study utilized a hybrid air-tendon actuation system, which has not yet been explored in existing literature for stiffness adaptation. To justify this hypothesis, a continuum mechanics model based on the nonlinear Cosserat rod method, incorporating hyperelastic material properties and accommodating large deformation kinematics, was developed and experimentally validated. This model demonstrated the feasibility of stiffness control through hybrid actuation. Initially, a static Cosserat rod model was developed and validated in a 2D context. Furthermore, the model was refined to incorporate the hyperelastic properties of the soft material, and its validity was established in 3D scenarios. Next, a dynamic model for the Cosserat rod was developed and validated using experimental data. Lastly, a parametric finite element method was used to optimize the geometry of the soft robot based on a defined goal function to reduce unnecessary radial expansion during inflation and enhance axial force transmission