Untethered, Dynamic Robotic Fabrics Enabled by Actively‐Rigid Variable Stiffness Fibers

Abstract A robot that uses fabrics as its core body material can be lightweight, compact, and highly flexible. Ideally, the robot's actuation, sensing, and structural support are provided by fiber‐based components, designed to integrate with the fabric's soft and conformable nature while preserving its fiber architecture. Typically, variable stiffness fibers are used for the structural elements, functioning as “bones” that can be turned on and off as needed. However, many variable stiffness fibers are passively‐rigid, only allowing the fabric to become soft when powered, while some require bulky external air or power supplies, making them untenable for untethered robotics. In this work, an electrically‐driven variable stiffness fiber is presented that performs a flat‐to‐curved geometry transition, providing a rigid load‐bearing structure when powered but remaining flexible otherwise. Design principles for pairing the actively‐rigid variable stiffness fiber with a materially compatible fiber‐based actuator are presented, and the actuator performance in different configurations is characterized. The variable stiffness fiber can be arranged into sturdy legs, stable enough for a robotic fabric to lift and hold its own battery pack and onboard electronics. This capability is demonstrated with a first‐of‐its‐kind fully‐untethered locomoting robotic fabric using two different quadruped gaits.