Researchers from University of Pennsylvania embodied logic in autonomous systems to enable them to respond to multiple stimuli
A team of researchers at the University of Pennsylvania’s School of Engineering and Applied Science used 3D printable fibrous composites to develop structures with geometries near bifurcation points associated with a transition between bistability and monostability. The structures rely on physical and chemical makeup to determine which of multiple possible responses to make in response to their environment. The structures do not require motors, batteries, circuits, or processors to switch between multiple configurations in response to pre-determined environmental cues. The research was led by Jordan Raney, assistant professor in Penn Engineering’s Department of Mechanical Engineering and Applied Mechanics along with Yijie Jiang, a postdoctoral researcher in his lab. The research was published in the journal Nature Communications on January 10, 2019.
The team used multi-material 3D printers to make these active structures with nested if/then logic gates. The timing of each gate can be controlled to enable complicated mechanical behaviors in response to simple changes in the environment. Bistability is defined by geometry and responsiveness by the material’s chemical properties. In a previous research, the team demonstrated 3D printing of bistable lattices of angled silicone beams. Bistable behavior relies on the angle of the beams and the ratio between their width and length, according to Raney. Elastic energy is stored in the material when the lattice is compressed. Controllable use of the environment to alter the geometry of the beams would fail bistable in the structure and release its stored strain energy.
The team infused the 3D-printed structures with glass or cellulose fibers that ran in parallel to the length of the beams. Similar to carbon fiber, this inelastic skeleton prevents the beams from elongating, while allowing the space between the fibers to expand, thereby increasing the beams’ width. The team found that more sophisticated shape-changing responses can be achieved with this geometric control in place, by altering the material the beams are made of. Active structures were made using silicone as it absorbs oil and hydrogels which absorb water. The researchers stated that heat- and light-sensitive materials can be added to offer materials that are responsive to even more specific stimuli.