BATE: A Bionic Ankle Tensegrity Exoskeleton With Adjustable Interaction Force and Motion Space

Tensegrity exoskeletons, integrating both rigid and flexible components, offer potential advantages over conventional rigid or flexible exoskeletons, particularly in terms of compliance, self-support, and self-balance. Inspired by the biotensegrity mechanism of human ankle joints, the bionic ankle tensegrity exoskeleton (BATE) provides multidegree of freedom, variable stiffness, and load support to assist human movement. However, the effectiveness of the BATE design depends on its seamless integration with the human body, particularly its interaction forces and precise motion alignment. To address this issue, a mathematical model of the equilibrium equation for the BATE exoskeleton was developed by employing the force density method. This model facilitated the creation of a semianalytical method to analyze interaction forces in various postures. Through the semianalytic interactive force algorithm, we determined the adjustable support force output range of the exoskeleton, from 0 to 50 N, and explored the influence of string stiffness and prestress on the support force output. Experimental results demonstrate that the modeling and semianalytical method can effectively evaluate interaction forces during walking gaits. Compared to not wearing an exoskeleton, the peak electromyogram (EMG) values in leg muscles decreased by 11.2% and 18.3% with the passive and active exoskeletons, respectively, while the mean EMG intensity decreased by 36.3% and 13.4% . This study provides valuable insights into interaction force control for next-generation tensegrity exoskeletons.