Self-folding kirigami robots will curl up in the face of disaster

A new form of robot unveiled this week could power daring search-and-rescue missions…by curling up at the first sign of heat.

The “active kirigami” robots, developed by a team at North Carolina State University, uses thin metal sheets to transform two-dimensional shapes into three-dimensional structures by applying heat. The findings were published this week in the journal Proceedings of the National Academy of Sciences.

“The potential applications could be related to miniature kirigami robots that could respond to environmental stimuli such as temperature, light, and moisture [et cetera] to fold themselves to move or transport,” Jie Yin, one of the paper’s authors and an assistant professor of mechanical and aerospace engineering at North Carolina State University, tells Inverse. “Its small size and compact shape is beneficial for confined space with potential applications in rescue [et cetera].”

“Kirigami” is similar to origami in that it involves folding paper, but the key difference is “kirigami” also involves cutting. The word was first introduced in that sense by Florence Temko in 1962 book Kirigami, the Creative Art of Papercutting. The word itself is pretty commonplace in Japanese though: “kiri” means “cut” and “gami” means “paper,” so previously the term simply meant “cut paper.”

Temko probably didn’t expect that, decades later, futuristic robots would take kirigami to all-new levels.

The team developed a robot that uses three layers. The two on the outside are heat-resistant, ensuring the bot doesn’t move in response to unexpected sources. The third, inner layer is a polymer that reacts to heat by contracting. Cuts that penetrate all the way through are used to control the machine’s movements, while etchings through the other layers enable the machine to manipulate its angle and the limits of its fold.

“We can make a 2D template with the same pattern of through-cuts and use it to create many different 3D structures by making slight changes in the etching,” Yin said in a statement. “This effectively makes the active kirigami sheets programmable.”

The initial proof of concept focused on small devices that can grip. It’s early days, but it’s easy to see how these shape-shifting machines could slot themselves into hard-to-reach places and complete otherwise impossible tasks.

These sort of advancements can enable more useful robots than ever before. Researchers in March 2017 developed an edible robot made of gelatin, which could explore more sensitive environments by wriggling around. In October, a team from UC San Diego developed soft, flesh-like actuators that can slim down machines’ joints by ditching the fluid pumps. Advancements in software from the likes of Boston Dynamics can also improve robotic motions.

The folding robot is the latest advancement in this field. Yin suggests the team can use all manner of materials for the inner layers. Although the proof of concept uses a polymer layer, the design could also use other reactive materials like photoactive liquid crystals. From here, the team hopes to further explore the potential range of applications.

>Abstract:

Kirigami (cutting and/or folding) offers a promising strategy to reconfigure metamaterials. Conventionally, kirigami metamaterials are often composed of passive cut unit cells to be reconfigured under mechanical forces. The constituent stimuli-responsive mate- rials in active kirigami metamaterials instead will enable potential mechanical properties and functionality, arising from the active control of cut unit cells. However, the planar features of hinges in conventional kirigami structures significantly constrain the degrees of freedom (DOFs) in both deformation and actuation of the cut units. To release both constraints, here, we demonstrate a universal design of implementing folds to reconstruct sole-cuts–based metamaterials. We show that the supplemented folds not only enrich the structural reconfiguration beyond sole cuts but also enable more DOFs in actuating the kirigami metasheets into 3 dimensions (3D) in response to environmental temperature. Utilizing the multi-DOF in deformation of unit cells, we demonstrate that planar metasheets with the same cut design can self-fold into programmable 3D kirigami metastructures with distinct mechanical properties. Last, we demonstrate potential applications of programmable kirigami machines and easy-turning soft robots.