Soft Morphing Textile Actuators using Shape Memory Effect

Abstract

Soft morphing structures execute biologically inspired motions more effectively through flexible body mechanisms than conventional rigid-bodied structures. Their softness and compliance allow them to mimic muscle-like biological locomotion and possess many degrees of freedom, compared with rigid bodies. To demonstrate the morphing in various modes, including three-dimensional (3D) volumetric transformation, textile actuators are presented based on woven and knitted structures. First, a woven type smart soft composite (SSC) consisting of shape memory alloy (SMA) wires and a glass fiber-reinforced composite was introduced for generating a large deformation using the inherent properties of woven textiles. The embedded SMA wires were divided into independently controlled groups to create asymmetrical bending through unequal power input and/or current feed times. By controlling the power input, symmetric/asymmetric actuation modes were achieved. To determine the characteristics of the woven SSCs, different configurations of the composite were tested in terms of the diameters of the SMA wires, numbers of embedded SMA wires, and numbers of glass-fiber fabric lamina. The proposed woven type SSC was implemented as the trailing edge of a spoiler on a small (⅛)-scale car and as variable winglets of an unmanned aerial vehicle. To confirm their aerodynamic performance, wind tunnel experiments were conducted under various wind speeds, angles of attack, and actuation modes of the soft morphing wings. Second, to demonstrate the morphing in various modes, including 3D volumetric transformation, a smart morphing knit was developed that was made from a thermally responsive fiber, allowing the creation of 3D morphologies with no auxiliary materials or an elastomeric matrix. A knitting method was used in the manufacturing process of the smart textile structure, and four combinations of loop patterns (plan, garter, rib, and seed patterns) were used to explore a variety of morphing shapes. Open and closed geometries of 14 knitting structures were used to characterize their morphing behaviors. Using the knitting methods, morphing flowers (a lily-like, a daffodil-like, a gamopetalous, and a calla-like flower) were fabricated and their blooming motion was demonstrated by controlling the current to actuate the petals selectively.