Self-folding with shape memory composites

Abstract

Origami-inspired manufacturing can produce complex structures and machines by folding two-dimensional composites into three-dimensional structures. This fabrication technique is potentially less expensive, faster, and easier to transport than more traditional machining methods, including 3-D printing. Self-folding enhances this method by minimizing the manual labor involved in folding, allowing for complex geometries and enabling remote or automated assembly. This paper demonstrates a novel method of self-folding hinges using shape memory polymers (SMPs), paper, and resistive circuits to achieve localized and individually addressable folding at low cost. A model for the torque exerted by these composites was developed and validated against experimental data, in order to determine design rules for selecting materials and designing hinges. Torque was shown to increase with SMP thickness, resistive circuit width, and supplied electrical current. This technique was shown to be capable of complex geometries, as well as locking assemblies with sequential folds. Its functionality and low cost make it an ideal basis for a new type of printable manufacturing based on two-dimensional fabrication techniques.

Self-folding shape memory laminates for automated fabrication

“…The increased control over assembly, as well as the integration of electrical circuitry, mean this approach is well suited to the self-folding of functional devices such as grippers. In addition, we have previously demonstrated bidirectional folding with this approach with the addition of a second SMP layer [23], [24].…”

“…While we have previously achieved some angle control by varying the overall width of the resistive heating elements [23], [24], we also found the heating duration to be important. Thus, here we fixed the heating element width at six millimeters (which simplifies design) and controlled the fold angle by adjusting the duration of current application.…”

“…We achieved this by adding an electrical circuit layer to the laminate which contains resistive heating elements [23], [24]. An additional advantage of this approach is the ability to precisely control a structure's fold sequence.…”

“…While this is a simple and inexpensive approach to self-folding, the single-material approach limits the strength and potential applications of the structures formed. Recently, we have demonstrated the use of similar SMPs, selectively actuated by resistive heaters, to realize self-folding robots and structures [23], [24].…”

Morphing in nature and beyond: a review of natural and synthetic shape-changing materials and mechanisms

“…This essentially reduces down into the earlier section on thermal triggers, with additional potential for control and integration [86,170]. Felton et al demonstrated this approaching using Joule heating to trigger a sequence of plates connected by SMP hinges to fold into both an origami crane [171] and a walking robot [172].…”