Bionic Ankle Tensegrity Exoskeleton With Considerable Load Bearing Capability

Rigid lower limb exoskeletons (LLEs) have limited flexibility while soft exosuits lack load bearing capability. To address this contradiction, inspired by ankle biotensegrity, a Bionic Ankle Tensegrity Exoskeleton (BATE) that combines rigid and soft structures is proposed to match the multi-degree-of-freedom (DOF) motion range of human ankle joint. Tensegrity structures utilize self-stress equilibrium and are self-supporting, enabling BATE to transfer loads to the ground via soft strings and provide load bearing capability. However, modeling and analyzing the load bearing capabilities poses challenges due to the high dimensionality and non-linearity of tensegrity structures, as well as complex human-exoskeleton interaction forces. Therefore, we establish a modeling and analysis method of BATE using the principle of minimum potential energy. We introduce bearing stiffness to evaluate load bearing capability. Finally, simulation and experiments consistently validate that the BATE can withstand an external interaction force in different joint postures and has considerable load bearing capability. The results indicate that the bearing stiffness of BATE depends on material stiffness. These features provide some biological hints to adjust bearing stiffness according to human body weight. Overall, this bionic design highlights advantages over current LLEs and provides new ideas for high-performance exoskeletons.