Intrinsic force sensing capabilities in compliant robots comprising hydraulic actuation

Knowledge of externally applied forces is crucial for compliant robotic manipulators in minimally-invasive and endoluminal robotic surgery for both patient safety and controllability of the device. We developed a novel continuum manipulator which comprises hydraulic actuation. In this work we investigate the use of the hydrostatic pressure feedback inside the inflatable actuation chambers to determine the normal and shear forces which are applied to the tip of the robot. For that purpose a nonlinear finite element model is derived and experimentally validated, showing a good approximation between experiment and simulation. The model is then used to derive descriptions for the normal and shear forces applied to the robot tip. The normal force estimation shows good results over the range of experimentally validated tip angles, while the shear force estimation shows good results for small tip deflection angles with an increasing error, with the tip orientation. The algorithm indicates good applicability to force control tasks as the forces are fast to compute.