Composite Soft Pneumatic Actuators Using 3D Printed Skins

The development of the field of soft robotics has led to the exploration of novel techniques to manufacture soft actuators. One subset of these- soft pneumatic actuators are conventionally developed from silicone, fabrics, and thermoplastic polyurethane (TPU). Each of these materials in isolation possesses limitations of low-stress capacity, low design complexity and high input pressure requirements, respectively. Combining these materials can overcome some limitations and maintain their desirable properties. In this manuscript, we explore one such composite design scheme using a combination of silicone polymers and TPU manufactured using fused deposition modelling (FDM). Silicone, which has high strain capacity, is used as the inner hermetic seal, while the 3D printed TPU acts as an external constraint that controls the deformation. The composite actuators have the advantage of being able to withstand higher stress than the silicone polymer and still being able to generate high deformations at modest pressures that TPU actuators are unable to achieve. In addition, the composite skins give the advantage of reconfigurability as the inner bladder, and the skin can both be modified to tune the properties of the final actuator. Effects of material selection and stiffness on the deformation and force properties of the composite actuators are also explored, along with variations in force output by changing the inner bladder. The practical utility of these 3D printed skins is demonstrated by showcasing a wearable elbow assistive device based on this technique.