Design of a Pneumatically Driven 3D-Printed Under-Actuated Soft Robot with Programmable Stiffness

Soft robotic technologies are laying the foundations for a wide range of applications involving manipulation, gripping, and locomotion. In particular, soft pneumatic actuators have been very popular for their high power-to-weight ratio and ability to yield significantly large motions. However, these actuators are usually limited in delivering reconfigurable deformation, limiting their versatility. A recent direction to rectify this limitation is to couple pneumatic actuation with active materials. Proof-of-the-concept designs has been developed to demonstrate that the actuator’s deformation characteristics could be configured by selectively softening structural elements in an ON-OFF manner. In this paper, following this idea, we propose a novel soft pneumatic actuator coupled with stiffness programmable polylactic acid (PLA) elements. The proposed design is based on heating wires embedded in the PLA elements. Changes in the elastic properties of PLA near the glass transition temperature (T<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</inf>) coupled with pneumatic actuation are exploited to activate the actuator’s variable stiffness features. This study shows that the stiffness of 3D-printed elements made of PLA can be tuned by means of temperature controlled heaters. The proposed actuator is able to extend by 19.5% of its original length and produce 15<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">◦</sup> angular deformation. We demonstrate the actuator’s ability to perform different reconfigurable orientations based on different temperature and pressure inputs. The proposed idea could be considered as an actuation unit that can deliver complex deformations when configured in multitudes.