Roboticizing fabric by integrating functional fibers

Abstract

Fabrics are ubiquitous materials that have conventionally been passive assemblies of interlacing, inactive fibers. However, the recent emergence of active fibers with actuation, sensing, and structural capabilities provides the opportunity to impart robotic function into fabric substrates. Here we present an implementation of robotic fabrics by integrating functional fibers into conventional fabrics using typical textile manufacturing techniques. We introduce a set of actuating and variable-stiffness fibers, as well as printable in-fabric sensors, which allows for robotic closed-loop control of everyday fabrics while remaining lightweight and maintaining breathability. Finally, we demonstrate the utility of robotic fabrics through their application to an active wearable tourniquet, a transforming and load-bearing deployable structure, and an untethered, self-stowing airfoil.

Keywords: active fibers; e-textiles; functional fibers; robotic fabric; smart textiles.

Fig. 1.

Robotic fabrics. (A) Rendering of a potential robotic fabric capable of locomotion. (B) Actualized robotic fabric demonstration. (C) Current robotic fabric vs. rendering of potential fully woven robot. (D) Fiber-form robotic components (from the left: sensors, actuators, and structural supports) can be combined in a variety of ways to create thin fabric-based machines.

Fig. 2.

SMA actuators. (A) SMA ribbon programmed to exhibit bending motion. (B) Sewn SMA ribbon used to actuate fabric body. (C) Couching method to affix SMA ribbon to a fabric substrate. (D) Initial round SMA wire. (E) Flattened SMA ribbon. (F) Bending an SMA against its programmed direction induces higher flexural stress and encourages the wire to twist instead. Error cloud is 95% confidence interval. (G) Round and flattened wires were subjected to forces at increasing out-of-plane angles to determine bending response. (H) A flattened ribbon will tend to bend and buckle in plane (green) and a round wire will tend to twist and bend out of plane (red). (I) Round SMA actuators tend to generate higher bending force than flattened actuators of comparable cross-section. Error bars are one SD.

Fig. 3.

VS fibers. (A) A shaped VS fiber supports a 20-g load. (B) VS fiber sewn onto a fabric substrate. (C) A VS fiber tethered by fabric is prevented from buckling outward, increasing support up to 50 g before legs begin slipping. (D) Neat epoxy VS fiber. (E) Neat epoxy cross-section. (F) FM composite cross-section. (G) FM composite VS fiber. (H) Hot and cold flexural modulus for both the neat epoxy and FM composite (46 vol % FM), with and without stainless steel yarn core used for joule heating. Error bars are SD. (I) Ultimate flexural strength of the VS fibers. (J) Measured thermal conductivity of the composite vs. volume percent of FM, compared with Bruggeman effective medium theory. Error bars are 95% confidence interval. (K) Free convection cooling of VS fibers. Experimental data are for neat epoxy specimens. Numerical simulations for both neat epoxy and FM composite had negligible difference (error cloud represents 95% CI). (Inset) Computed cross-sectional thermal gradient for both 0 and 50 vol % FM fibers after 7 s of cooling from 65 °C. (L) Numerical simulation results for a “worst-case” heating scenario, with the heating core center offset to two-thirds of the VS fiber diameter. (Inset) Computed cross-sectional thermal gradient after 6 s of heating at 13 W/m.

Fig. 4.

Conductive ink sensors. (A) The carbon black/PDMS/ethanol emulsion is printed directly onto the fabric. The surface conductivity is sufficient such that printed sensor blocks can be electrically connected by sewing over them with conductive thread. (B) A microscope image of ink-coated knitted spandex fabric. (C) Porosity measurement of neat, unstrained fabric. (D) Porosity of inked fabric. (E) Porosity of inked fabric after stretching. (F) A simple actuator-sensor device curls up and down, generating a sensor signal dependent on device curvature. (G) The curling device follows the control signal by modulating the power output to the SMA actuators. Each sensor is actively used only when the corresponding fabric face is in extension.

Fig. 5.

Robotic fabric demonstrations. (A) Robotic fabric tourniquet. (B) Tourniquet is buttoned about a foam body. It reacts to a damaged circuit by contracting and holding a tightened “clover-shape” pose. (C) Thermal image of the tourniquet as VS fibers soften. (D) Thermal image of activated SMA actuators constricting. (E) Robotic fabric “pop-up” table. (F) From an initial flat state, the table is able to stand up, stiffen into a load-bearing platform, and then collapse under a load as it softens and actuates back into its initial flat configuration. (G) Fabric “pop-up” table is ∼2 mm thick. (H) Activation and softening of table “leg” VS fibers. (I) Activation of SMA actuator wire, causing table to stand up. (J) Robotic fabric wing in self-stowed position. (K) Robotic fabric wing curls and uncurls from deployed, open state into a compacted, stowed state. (L) Robotic fabric wing in deployed position. (M) Activation and softening of wing VS fibers. (N) Activation of curling SMA wires.