|A fast-response, stiffness-tunable (FRST) soft actuator is fabricated by hybrid multi-material 3D printing. Researchers at Shanghai Jiao Tong University developed the process to create these robotic actuators to provider safer robots for human interaction and proximity. (Image source: Shanghai Jiao Tong University)|
Late last year a horrific robotic mishap in a Chinese factory that left a worker impaled with spikes demonstrated that working close to or interacting with robots with rigid parts can be extremely dangerous. For this reason, researchers are advancing the design and development of robots with soft actuators and other parts that can perform on par with rigid ones.
A cross-institutional and disciplinary team from the Singapore University of Technology and Design (SUTD) and Shanghai Jiao Tong University (SJTU) developed a new method for manufacturing what they call “fast-response, stiffness-tunable” (FRST) soft actuators that can show unprecedented responsiveness in load-bearing tasks. The researchers published a paper on their work in the journal Advanced Functional Materials.
Soft robots can adapt easily to surroundings and offer safe, coexisting interaction with humans. However, it’s typically been challenging for soft robots to perform load-bearing tasks as well as their more rigid counterparts.
That may change with the new actuators, which are made from shape memory polymers (SMPs) and designed and developed using hybrid multi-material 3D printing. According to the research paper, the actuators can complete a softening-stiffening cycle within 32 seconds, showing competency to lift objects similarly to robots made from rigid parts.
Key to the design is the use of SMPs, which are both capable of reversibly changing stiffness by two to three orders of magnitude and compatible with 3D printing. However, in the past, SMP-based soft actuators generally were limited by slow responses, small deformations, and difficulties in automated fabrications with micro-features, according to the researchers.
The new work solved these issues by combining commercial inkjet multi-material 3D-printing technology with the direct-ink writing approach for fabrication, said Qi (Kevin) Ge, an assistant professor in SUTD's Science and Math Cluster and a co-leader of this project.
Researchers achieved the actuator’s stiffness tunability using an embedded SMP layer, while embedding heating and cooling elements enabled the fast response of the device, Ge said. Indeed, the integration of the SMP layer into the actuator body enhanced its stiffness by up to 120 times without sacrificing flexibility and adaptivity.
Specifically, researchers used a deformable conductive circuit printed with a silver nanoparticle ink to activate the rubbery state of the SMP by localized Joule-heating. Once the actuator was deformed with pressurized air, the process uses coolant to driven through a fluidic channel to lock the geometry and lower the temperature of the SMP, Ge said.
"The deformed actuator in its stiff state can perform load-carrying tasks, even after releasing the pressurized air,” Ge said. “More importantly, a heating-cooling cycle can be completed within about half a minute, which is the fastest rate reported, to our knowledge.”
To demonstrate the success of their method, the team devised a robotic gripper with three FRST actuators that can grasp and lift objects with arbitrary shapes and various weights spanning from less than 10 grams to up to 1.5 kilograms, Ge said. They used computational models to simulate the mechanical and thermal-electrical behaviors of the FRST actuator to guide its design and provide insights into enhancement of load capacity, he added.
Elizabeth Montalbano is a freelance writer who has written about technology and culture for 20 years. She has lived and worked as a professional journalist in Phoenix, San Francisco and New York City. In her free time she enjoys surfing, traveling, music, yoga and cooking. She currently resides in a village on the southwest coast of Portugal.
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