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Researchers at Tianjin University in China have 4D printed a self-propelled soft robot that can roam on its own.
The tubular robot is made of a material called liquid crystal elastomer, which assembles itself when exposed to heat. The device uses cleverly programmed folding patterns to generate pressure in its own body, allowing it to roll like a log. In addition to traversing a plane, the 4D printed soft robot can also complete more challenging tasks, such as climbing a 20° slope, or even dragging a load up to 40 times its own mass.
"Like an insect with only tentacles, a robot can overcome a small obstacle. But when the obstacle is too high, it will turn back," said Wei Feng, a materials scientist at Tianjin University and senior author of the study. "The whole process is spontaneous, without human intervention or control."
Liquid crystal elastomer for 4D printing
Liquid crystal elastomer is a flexible plastic material that can shrink when heated. This makes it an excellent class of materials for reversible drive applications such as soft robots, especially because they can be used to generate large work densities.
In the case of a soft robot at Tianjin University, the researchers 3D printed a flat rectangular liquid crystal elastomer sheet and heated the surface below it to 160°C or higher. At this temperature, the heat from the surface below causes the robot to twist itself into a tubular shape similar to a coil spring. Further contact with the heated surface creates strain in the material, causing it to roll on its own through peristaltic motion.
The change in shape after printing (caused by heat) is what makes the device 4D printing, because the fourth dimension of time is added to the equation.
After the printout, the software robot passed a series of performance tests. Researchers have found that it exhibits a very strong driving force, enabling it to climb a 20° slope and carry a load that is much heavier than itself. In the end, the team 4D printed several robots and made them compete with each other, and found that the length of the robots had a huge impact on their speed. One of the longer robots spans 10 cm in length and reaches 48 cm/min on a flat surface.
“We processed liquid crystal elastomers into samples of various shapes through 4D printing, and stimulated these samples with light, heat, and electricity to observe their responses,” Feng added. "In addition to deformation, we also found many interesting driving phenomena."
In terms of future applications, Tianjin researchers hope to see their soft robots work in narrow spaces such as pipelines or under extreme conditions above 200°C. Feng concluded: "We hope that the soft robot is no longer limited to simple actuators, but can only change shape at a fixed position."
More details of the research can be found in the paper entitled "4D printed cordless self-propelled soft robot with tactile perception: rolling, racing and exploring".
The design freedom granted by 3D printing makes this technology a very useful tool for new applications such as soft robotics. Earlier this year, Harvard University researchers also used 3D printing to develop a school of soft robotic fish that can swim in complex patterns without the help of Wi-Fi or GPS. Inspired by the unique surgeonfish that inhabit the reef, the team’s "Bluebots" have four fins for precise navigation, as well as an LED and camera system, allowing them to swarm without collisions .
Elsewhere, researchers at Linköping University in Sweden have previously developed a set of microactuators for soft microrobots using custom extrusion-based 3D printers. The actuator contains an electroactive polymer that changes shape after printing in the presence of a charge, giving them a 4D function.
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The featured image shows the 3D printing and heating of the soft robot. The picture comes from Tianjin University.
With a degree in mechanical engineering, Kubi Sertoglu combines a passion for writing with a technical background to provide the latest news and reviews in the field of additive manufacturing.
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