Single chamber multiple degree-of-freedom soft pneumatic actuator enabled by adjustable stiffness layers

Soft pneumatic actuators promise simple, adaptable, and safe manipulation, but the nature of pneumatic circuits limits the scalability of this approach. This paper introduces a method to augment the degrees-of-freedom of soft pneumatic actuators without increasing the number of independent pressure sources or complex valving networks. Our method achieves multiple degree-of-freedom actuation from a single soft pneumatic chamber by utilizing adjustable stiffness layers based on a thermoplastic polyurethane shape memory polymer (SMP), which changes stiffness when thermally activated. We incorporate SMP layers into a soft pneumatic actuator, allowing multiple degrees of soft deformation to be achieved from a single pressure source by selective activation of SMP layers. A custom printed circuit board acts as a control unit to modularize and enable closed-loop control of the proposed pneumatic actuator. We validated our proposed system and method by varying the temperature of the SMP layer on one side of the actuator while keeping the other side stable near room temperature and observed an increase in bending angle of the pneumatic actuator as a function of temperature. Furthermore, we connected two actuators in series and demonstrated independent actuation, allowing the actuators to form different shapes with a single pressure source. Our results show that the proposed method can augment the degrees of freedom of soft pneumatic actuators as an alternative to multi-chamber or multi-valve systems.