Design Optimization for the Stability of Concentric Tube Robots

Concentric tube robots are catheter-sized continuum robots that show dexterous movement for minimally invasive surgical procedures. However, one of the major challenges to the practical usage of concentric tube robots is their instability, which potentially leads to the risk of tissue rupture. The snapping problem is caused by tubes having a high bending to torsional stiffness ratio (BTSR). Past efforts have shown that anisotropic patterning on tubes can alleviate the snapping problem. This research investigates the design optimization of patterns to minimize BTSR while satisfying stiffness constraints. Using topology optimization methods, rhombus-shaped patterns were identified as the ideal shape for stability. The generated designs were validated through finite element analysis and experimental testing to show the change of BTSR and the elimination of the snapping problem. Extensive parametric study is performed to analysis the sensitivity of the design parameters and provide the design guidelines. While satisfying the constraints, the proposed design method demonstrated 0.28 of BTSR with a rhombus angle of 60 degrees and a volume fraction of 0.55. The optimized design potentially improves the workspace and versatile trajectories of concentric tube manipulators.