The tentacle robot can gently grasp delicate objects.

If you've ever played the claw game at an arcade, you'll understand how difficult it is to grab and hold onto objects with robotics grippers. Imagine how terrifying that game would be if you were attempting to grab a fragile piece of endangered coral or a priceless artifact from a sunken ship instead of plush stuffed animals.

Soft gripper grasps succulent. Credit: Harvard Microrobotics Lab/Harvard SEAS
Soft gripper grasps succulent. Credit: Harvard Microrobotics Lab/Harvard SEAS

To grasp fragile or irregularly shaped objects, most robotic grippers today rely on embedded sensors, complex feedback loops, or advanced machine learning algorithms, in combination with the operator's skill. However, Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) researchers have demonstrated an easier way.

Taking inspiration from nature, they created a new type of soft, robotic gripper that entangles and ensnares objects in the same way that jellyfish collect stunned prey. Individual tentacles or filaments are ineffective on their own. However, when combined, the filaments can grasp and securely hold heavy and irregularly shaped objects. The gripper wraps around objects using simple inflation and does not require sensing, planning, or feedback control.

The findings were reported in the Proceedings of the National Academy of Sciences (PNAS).

"We wanted to reimagine how we interact with objects with this research," said Kaitlyn Becker, a former graduate student and postdoctoral fellow at SEAS and the paper's first author. "We designed a gripper that is greater than the sum of its parts and a grasping strategy that can adapt to a range of complex objects with minimal planning and perception by taking advantage of the natural compliance of soft robotics and enhancing it with a compliant structure."

Becker is a Mechanical Engineering Assistant Professor at MIT.

The ability of the gripper to entangle itself with the object it is attempting to grasp accounts for its strength and adaptability. The foot-long filaments are made up of hollow rubber tubes. When the tube is pressurized, it curls like a pigtail or straightens like hair on a rainy day because one side of the tube has thicker rubber than the other.

The curls knot and entangle with one another and with the object, with each entanglement strengthening the hold. While the collective hold is strong, each individual contact is weak and will not harm even the most delicate object. The filaments are simply depressurized to release the object.

The researchers used simulations and experiments to test the gripper's effectiveness, picking up a variety of objects such as houseplants and toys. The gripper could be used in real-world applications such as agricultural production and distribution of soft fruits and vegetables, delicate tissue in medical settings, and even irregularly shaped objects in warehouses such as glassware. 

Professor L. Mahadevan's research on the topological mechanics of entangled filaments is combined with Professor Robert Wood's research on soft robotic grippers in this new approach to grasping.

"Entanglement allows each highly compliant filament to conform locally with a target object, resulting in a secure but gentle topological grasp that is relatively independent of the details of the nature of the contract," explained Mahadevan, the Lola England de Valpine Professor of Applied Mathematics in SEAS, Organismic and Evolutionary Biology, and Physics in FAS, and co-corresponding author of the paper.

"This new approach to robotic grasping complements existing solutions by replacing simple, traditional grippers that require complex control strategies with extremely compliant, morphologically complex filaments that can operate with very simple control," said Wood, co-corresponding author of the paper and the Harry Lewis and Marlyn McGrath Professor of Engineering and Applied Sciences. "This approach broadens the range of what robotic grippers can pick up."*


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