Hao Zheng, Molei Wu, and Xiangrong Shen
Robotic prostheses, assistive robotics, pneumatic actuation
For a powered transtibial prosthesis, elasticity plays an important role in its interaction with the amputee user and the environment. However, the most commonly used prosthetic actuator, DC motor, does not provide elasticity by itself, and thus has to be complemented with physical and (controller-implemented) artificial elastic elements. In this paper, a novel pneumatic variable series elastic actuator (VSEA)-powered transtibial prosthesis is presented. The pneumatic VSEA has a physically existing elasticity generated by the compressibility of the working fluid, and thus eliminates the need for additional elastic elements. Furthermore, it can be modelled as a variable spring with controllable stiffness and equilibrium point, enabling the direct implementation of the finite-state impedance control (FSIC) of the powered prosthesis (no closed-loop force control needed). Details on the design and elasticity modelling of the pneumatic VSEA-powered prosthesis are provided in this paper, followed by the formulation and simulation of the directly implemented FSIC prosthesis controller. Human subject testing results show that the prosthesis is able to provide a natural gait in treadmill walking with minimum control action from the directly implemented FSIC controller, demonstrating the unique advantages of this novel approach.
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