Variable stiffness and shape prosthetic socket based on layer jamming technology

Abstract

To obtain functional and comfortable lower limb prostheses, major attention must focus on the physical interface constituted by the prosthetic socket. Indeed, the rigid socket is in contact with residual limb tissues, that are much softer yet variable depending on daily activities. For adapting the stiffness and shape of the prosthetic interface to the physiological changes of the residual limb, the layer jamming principle appears a really promising solution. Therefore, a new smart transfemoral socket with integrated soft actuators is presented. Each actuator is constituted by one inflatable chamber and two layer jamming ones, optimized in terms of achievable stiffness to be integrated into the socket. A control unit was designed to allow for shape and stiffness changes of the actuator. The weight of the control unit resulted equal to 450 g with dimensions equal to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$43\times 140\times 80\ \text{mm}^{3}$</tex> . The final thickness of the actuator was 10.5 mm. Thus, the proposed design enables the wearability of the system. Preliminary tests were carried out evidencing a 15-times increment of the layer jamming chamber stiffness from the soft state at atmospheric pressure to the stiff state at 31 kPa absolute pressure. In addition, a maximum displacement of the integrated multi-chamber actuator equal to 21.30 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\pm 0.85$</tex> mm and the functionality of the system have been demonstrated.