A 3D-printed actuator, made from photopolymerizable elastomeric material, uses pneumatics to mimic an octopus tentacle—without requiring complex internal parts. The work done by a team of engineers at Cornell University was published in a special issue of Bioinspiration and Biomimetics Journal, which focuses on bioinspired soft robots. The report claims that the actuator adopts the function of muscular hydrostats with response times that are comparable to living muscle. Other muscular hydrostat systems are found in tongues and elephant trunks.
The actuator is especially groundbreaking because it is a non-homogenous piece that can be printed using layer-by-layer, digital-mask-projection stereolithography. This method employs a single nozzle and directs visible light at different intensities to cure the photopolymerizable elastomer with different levels of viscosity.
Watch the demonstration of the pneumatic tentacle in the following video.
Pneumatics and Hydrostat Pressure
Stacked chambers arranged in separate columns are filled with fluidic elastomer, so that they will maintain the same volume while experiencing changes in pneumatic pressure. In turn, cross-section and length of the chambers inversely change during pressurization, enabled by the pleated shape of the actuator.
During bending, pressure is increased in one chamber and decreased in another. For the column of chambers that experience decreased pressure, a pleat enables an increase in cross-section and shortens in length. Meanwhile, the pressurized column elongates and cross-section decreases in response to heightened pressure. The internal, incompressible fluid eliminates the need for skeletal structure.
The most developed prototype includes two layers that contain pairs of antagonistic chambers aligned at 90 degrees to achieve four degrees of freedom. Each pair is pressurized by its own pneumatic source, both of which supply opposite signs of pressurization for even bending. Other degrees of motion are possible with this device, such as torsion with the introduction of helically arranged chambers.