Harnessing the Curvature of Weft-knit Textiles to Control their Mechanics, Kinematics, and Shape-changing Response

Abstract

Curved elastic shells can be fabricated through molding or by harnessing residual stresses. These shells often exhibit snap-through behavior and multistability when loaded. We present a unique way of fabricating curved elastic shells that exhibit multistability and snap-through behavior, weft-knitting. The knitting process introduces internal stresses into the textile sheet, which leads to complex 3D curvatures. We explore the relationship between the geometry and the mechanical response, identifying a parameter space where the textiles are multistable. We harness the snapping behavior and shape change through multistability to design soft conductive switches with built-in haptic feedback, and incorporate these textile switches into two wearable devices and one reconfigurable lamp. This work will allow us to harness the nonlinear mechanical behavior of textiles to create functional, soft, and seamless devices. Weft knit textiles are growing in popularity as materials for soft robotic applications due to their scalability and near infinite mechanical tunability. We leverage the benefits of 3D weft knitting to develop a novel method of manufacturing small scale (5-8 mm) pneumatic actuators that can be embedded across a distributed textile surface. Weft knitting (i.e., intarsia) enables seamless transitions between contrasting yarns and textile structures, which increases manufacturing resolution for small-scale actuators. Additionally, weft knitting enables mechanical property tunability beyond what is available off the shelf, enabling customizable actuation behavior. We demonstrate that 3D knit textile actuation properties, such as blocking force, free displacement, and bending stiffness, can be tuned by manipulating actuator design parameters, including (1) yarn tensile stiffness, (2) textile structural strain, (3) local textile geometry, and (4) input pressure. To demonstrate the manufacturability and scalability within a 3D wearable form factor, we build a haptic glove prototype with surface embedded actuation to mimic the sensation of touching and grasping virtual objects.