18/07/2022
Ad Spijkers
Inflatable actuators use origami principles to deform in complicated ways.
Inflatable soft actuators that can change shape with a simple increase in pressure can be powerful, lightweight and flexible components for soft robot systems. But when pressurized these actuators always deform in the same way. To improve the functionality of soft robotics, it is important to enable additional and more complex forms of deformation in soft actuators.
Researchers at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) in Allston and Cambridge, Massachusetts, have taken inspiration from origami to create inflatable structures that can bend, twist and move in complex different ways, from a single pressure source.
From monostable to bistable
Most of today's inflatable soft drives are monostable: they require a constant pressure to maintain their inflated state. When the pressure drops, the structure deflates to its only stable form. An inflated monostable always takes on the same unfolded shape and returns it to the same original shape when the pressure drops. In their research work, the scientists use bistable origami building blocks to get around this limitation.
Bistable origami blocks are stable in two different configurations and do not require constant pressure to remain deployed. The research team used a classic origami pattern known as the Kresling motif. This is characterized by alternating mountain and valley folds on a cylinder to form triangular cells.
Defect
The researchers first made simple monostable modules from the Kresling pattern. To unlock bistability, they added a defect to the origami pattern. An additional node creates a dome with four triangles that can jump in or out when a certain amount of negative or positive pressure is delivered.
The researchers first inflate the structure with a specific pressure to inflate specific cells that remain open even when the pressure drops. Because they are breaking symmetry, the researchers can use a vacuum in this new configuration to induce bending, contraction or rotation. Then they inflate the structure to a second pressure to deploy additional cells that unlock completely different deformations when they vacuum again.
By putting together different modules and tuning their geometry to break at different pressures, the researchers create structures that can create complex shapes and deformation modes that can be pre-programmed and activated with just one pressure source.
Twelve modules
The researchers built an actuator with twelve different modules and showed that it can perform up to eight different, complex movements. They also developed an algorithm that can identify the optimal combination of modules for the desired deformation modes.
Since the mechanics in the system are driven by geometry, the approach could lead to applications at different scales. By simply increasing and decreasing pressure, inflatable actuators can perform complex tasks without the need for cables, motors or electricity. This is interesting for many applications, including surgical procedures or space exploration.
Photo: Harvard SEAS