Researchers at North Carolina State University developed a robotic gripping device that is gentle enough to pick up a drop of water, strong enough to pick up a 14.1 lb. weight, dexterous enough to fold a cloth, and precise enough to pick up microfilms that are 20 times thinner than a human hair. The researchers integrated the device with a myoelectric prosthetic hand that allowed the gripper to be controlled by the electrical signals produced by muscles in the forearm.
“It is difficult to develop a single, soft gripper that is capable of handling ultrasoft, ultrathin, and heavy objects, due to tradeoffs between strength, precision, and gentleness,” says Jie Yin, PhD, corresponding author of a paper on the work and an associate professor of mechanical and aerospace engineering at the university. “Our design achieves an excellent balance of these characteristics.”
The design for the grippers builds on an earlier generation of flexible, robotic grippers that drew on the art of kirigami, which involves cutting and folding two-dimensional sheets of material to form three-dimensional shapes.
“Our new grippers also use kirigami, but are substantially different, as we learned a great deal from the previous design,” says Yaoye Hong, PhD, coauthor of the paper. “We’ve been able to improve the fundamental structure itself, as well as the trajectory of the grippers—meaning the path at which the grippers approach an object when grabbing it.”
The new design can achieve high degrees of strength and gentleness because of how it distributes force throughout the structure of the gripper.
“The strength of robotic grippers is generally measured in payload-to-weight ratio,” Yin said. “Our grippers weigh 0.4 grams and can lift up to 6.4 kilograms. That’s a payload-to-weight ratio of about 16,000. That is 2.5 times higher than the previous record for payload-to-weight ratio, which was 6,400. Combined with its characteristics of gentleness and precision, the strength of the grippers suggests a wide variety of applications.”
“This gripper provided enhanced function for tasks that are difficult to perform using existing prosthetic devices, such as zipping certain types of zippers, picking up a coin, and so on,” said Helen Huang, PhD, coauthor of the paper and Jackson Family Distinguished Professor in the Joint Department of Biomedical Engineering at NC State and the University of North Carolina at Chapel Hill.
“The new gripper can’t replace all of the functions of existing prosthetic hands, but it could be used to supplement those other functions,” Huang said. “And one of the advantages of the kirigami grippers is that you would not need to replace or augment the existing motors used in robotic prosthetics. You could simply make use of the existing motor when utilizing the grippers.”
In proof-of-concept testing, the kirigami grippers were used with the myoelectric prosthesis to turn the pages of a book and pluck grapes off a vine.
Another benefit of the new technology is that its characteristics are driven primarily by its structural design, rather than by the materials used to fabricate the grippers, meaning it could be made of biodegradable materials for use in applications such as handling food or biomedical material.
“We think the gripper design has potential applications in fields ranging from robotic prosthetics and food processing to pharmaceutical and electronics manufacturing,” Yin says. “We are looking forward to working with industry partners to find ways to put the technology to use.”
Editor’s note: This story was adapted from materials provided by North Carolina State University.
The open-access paper, “Angle-programmed tendril-like trajectories enable a multifunctional gripper with ultradelicacy, ultrastrength, and ultraprecision,” was published in Nature Communications.
To watch a video of the device in action, visit the Yin lab at NCSU’s YouTube channel.
