Origami Structures Lead to Adjustable Stiffness in Robots

New research out of Arizona State University demonstrates how curved origami structures can lead to tunable flexibility in robots. Tunable flexibility allows a robot to adjust its stiffness based on the task at hand, which in the past has proven to be difficult to implement with simple designs.

Hanqing Jiang is a mechanical engineering professor at the university and lead author of the paper titled “In Situ Stiffness Manipulation Using Elegant Curved Origami.” The work was published in Science Advances.

“The incorporation of curved origami structures into robotic design provides a remarkable possibility in tunable flexibility, or stiffness, as its complementary concept,” Jiang said. “High flexibility, or low stiffness, is comparable to the soft landing navigated by a cat. Low flexibility, or high stiffness, is similar to executing a hard jump in a pair of stiff boots.”

Operational Difference

Jiang compared the operational difference offered by curved origami to that of sports cars versus more comfort-focused vehicles.

“Similar to switching between a sporty car mode to a comfortable ride mode, these curved origami structures will simultaneously offer a capability to on-demand switch between soft and hard modes depending on how the robots interact with the environment,” he said.

Within the field of robotics, there are different stiffness modes such as high rigidity, which is crucial for lifting heavy weights. High flexibility is relied on for impact absorption, and negative stiffness, which is the ability to released stored energy like a spring, is used for sprinting.

On-Demand Flexibility

For robots that require rigidity, they are often bulky. However, curved origami allows for them to operate on an expanded stiffness scale, meaning on-demand flexibility.

The team’s research focused on combining the folding energy at origami creases with the panel bending, which is tuned by moving along multiple creases between two points. With curved origami, a single robot is capable of undertaking various movements. For example, the team developed a swimming robot that has a range of nine different movements, such as fast, slow, medium, linear, and rotational. In order to accomplish any of these, the creases just need to be adjusted.

Besides robotics, the principles laid out in the research could help design mechanical metamaterials in electromagnetic, automobile, and aerospace industries. It could also prove to be useful in the creation of biomedical devices.

“The beauty of this work is that the design of curved creases, and each curved crease corresponds to a particular flexibility,” Jiang said.

Other contributing authors to the research include Hanqing Jiang, Zirui Zhai, and Lingling Wu from the School for Engineering.