Researchers at the Department of Mechanical Engineering, Seoul National University, led by Professor Kyu-Jin Cho—Director of the Human-Centered Soft Robotics Research Center and a founding member of the SNU Robotics Institute (SNU RI)—have applied the principle of interlacing to an origami-inspired structure and developed a "Foldable-and-Rollable corruGated Structure (FoRoGated-Structure)" that can be smoothly folded and rolled up for compact storage while maintaining very high strength when deployed. The study was published in the internationally renowned journal Science Robotics on November 26.
Rolling a structure around a central hub—similar to how a tape measure is stored—is an effective way to achieve compact storage. In such mechanisms, the structure typically has a flat cross-section in the storage phase, allowing it to wrap smoothly around the hub, and then transforms into a corrugated cross-section in the deployed phase to suppress bending and sagging. This is analogous to how a flat sheet of paper is flexible, but once folded into a zigzag corrugation, the adjacent faces restrain each other's deformation and the folded paper becomes strong enough to support significant loads.
However, when a conventional corrugated structure is folded into multiple layers and then wound around a hub, the material thickness causes a perimeter (length) mismatch between inner and outer layers, which leads to buckling and wrinkling. For this reason, such structures are usually unfolded into a single flat layer before being wrapped around the hub. As the scale of the corrugation increases, the structural strength improves, but the required storage width grows, resulting in a fundamental trade-off between strength and compactness.
To overcome this limitation, the research team introduced the interlacing principle into the corrugated structure. An interlacing structure connects multiple elements not by rigidly bonding them, but by crossing and interlocking them so that gaps between elements allow sliding and rearrangement, while along the interlocked direction the elements share loads and maintain shape.
In their design, the researchers arranged metal strips in parallel along the length and, instead of bonding them to each other, tightly wove them with ribbons to form loop-shaped interlacing joints. These joints provide dense constraints between neighboring strips, forming a stiff corrugated folding structure, while at the same time allowing local sliding of the strips through the ribbon loops. As a result, the structure can be folded into multiple corrugated layers and still be wound smoothly around the hub. The sliding motion alleviates stress concentrations arising from the perimeter mismatch between layers, and the high density of interlacing enhances cross-sectional stability, enabling high strength and stiffness in the deployed state.
The team summarized, "By using ribbons to interlace stiff structural strips, we demonstrated that even a corrugated structure with many folds can be stacked into multiple layers and still be rolled up smoothly for compact storage."
Going beyond theoretical analysis, the researchers developed a single-motor-driven "extendable robotic arm" based on the FoRoGated-Structure and demonstrated its applicability to several deployable robotic systems.
First, they mounted the arm on a small mobile robot with a height comparable to a robot vacuum cleaner. In the stored state, the robot maintains a very low profile, but when the arm is deployed, it can perform high-reach tasks, such as organizing items on shelves or pressing elevator buttons.
Second, they demonstrated a deployable mobile 3D-printing robot. A mobile base with a diameter of approximately 1 meter and a height of approximately 1 meter travels to a target location, and during deployment its frame transforms from a compact triangular column (equilateral triangle side 420 mm, height 730 mm) into a large tetrahedral frame with a base edge of about 3.2 meters and a height of about 3.4 meters. Using this deployed frame, the robot can 3D-print structures approximately 2.5 meters tall.
These demonstrations show that the FoRoGated-Structure is well suited to applications where systems must be stored in a small volume yet must withstand substantial working loads after deployment.
Co-first authors Sun-Pill Jung (currently at Seoul National University) and Jaeyoung Song (currently at HD Korea Shipbuilding & Offshore Engineering) explained, "We applied the interlacing principle, in which elements cross and interlock like woven fabric, to folding structures so that the perimeter mismatches in multi-layer structures can be absorbed structurally. As a result, we realized an origami-inspired structure that can be folded and rolled up in a dual-compression method for compact storage, while maintaining high strength through dense interlacing in the deployed state." "We often look to a single morphology—the humanoid—for solutions, but many real-world problems depend on the specific environment and task," said Prof. Kyu-Jin Cho. "Our results show that robots which reconfigure and deploy to fit the space and the task can serve as a practical platform for Physical AI."
This research has been supported by the National Research Foundation of Korea (NRF) Grant funded by the Korean Government (MSIT) (RS-2023-00208052) (to K-J.C.).
※ Video link (Youtube): https://youtu.be/FysgitFVVBs
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• What motivated this research? How did you become interested in this topic?
Between 2020 and 2021, we worked on a national research project related to solar sails, where we strongly felt the need for rollable structures that are both strong and highly compressible. Even after that project ended, we kept thinking about this challenge. One day, we noticed how a thick book can be rolled relatively smoothly because its pages are separated, and that gave us the idea: "If we can introduce controlled sliding into a folding structure, maybe we can store it much more compactly."
As we received feedback from colleagues, it became clear that to highlight what limitations our structure overcomes, we needed large scale demonstrations. This pushed us to imagine robots that could autonomously print shelters on the Moon. From there, we decided to build meter-scale deployable 3D-printing robots as a step toward that vision.
• What are the next steps? What should other researchers work on?
Our current prototypes are made by weaving ribbons into the structure. This approach is suitable for laboratory-scale fabrication but is not yet ideal for mass production, and the ribbons tend to wear and tear with repeated use. While this is acceptable for proof-of-concept demonstrations, practical deployment will require improvements in both manufacturability and durability.
If we can significantly enhance production efficiency and service life, we see strong potential for real-world applications, such as modular robotic arms for consumer robot vacuum cleaners and mobile "house-printer" robots that fabricate building-scale structures on site.
• Can you explain the developed structure in simple language, as if talking to a child?
This robot arm is like a tape measure. When you use it, it stretches out long, and when you don't, it rolls up into a small, flat shape. When it stretches out, folded ridges (like paper folds) appear and it becomes a strong, long arm. When you put it away, those folds stack up and then roll up, so the arm can be stored very thin and compact. Normally, if you fold a sheet of paper many times and then try to roll it, the inside part gets crumpled and it doesn't roll nicely. We solved this by designing special folding joints so that the folded parts can slide a little and rearrange themselves instead of getting wrinkled. That's why the structure is soft and easy to store, but strong when you use it.
With this structure, even a small robot can reach up to high shelves to handle objects, and by using several of these arms together, a robot can build a very large frame. A robot equipped with such a frame can even perform 3D printing inside the large structure made from this mechanism.
