Engineers at the University of California San Diego have developed a robot gripper inspired by the childhood habit of unspooling measuring tape to see how far it will extend before bending. According to the researchers, the gripper would be a particularly good fit for agricultural applications, as its extremities are soft enough to grab fragile fruits and vegetables.
The device, which is also low-cost and safe around humans was dubbed GRIP-tape by the team (GRIP: Grasping and Rolling In-Plane).
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Building the ideal robotic gripper is still a work in progress. Existing grippers that can expand are bulky because they need additional mechanisms to get gripping appendages to expand. The gripper the UC San Diego team developed solves this problem because the tape is both robust and flexible, can be stored in a small container when retracted and can reach far when extended. After a series of trial-and-error experiments, the engineers determined that the best configuration for a gripper is actually two of the tapes bound together with adhesive.
‘We like to look for non-traditional, non-intuitive robot mechanisms,’ said Nick Gravish, a faculty member in the Department of Mechanical and Aerospace Engineering. ‘The tape measure is such a wonderful structure because of its combined softness and stiffness.’
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The gripper has two ‘fingers’, made of two spools, each of which is made of two rolls of measuring tape bound together. Each spool is rolled up, in a compact configuration, with only a small part extending out in a triangle shape to form a finger. These triangle sections are controlled by four motors each, which control the finger’s motion. Each finger can move independently. The triangle sections can lengthen to reach objects that are farther away. They can also retract to bring objects closer to the robot arm the gripper is mounted on.
The researchers had already worked with measuring tape as part of a National Science Foundation grant to investigate soft materials that could bend while holding their shape. Measuring tape is springy – you can bend it any way you want and it goes back to its original state. It’s also made of steel, which is both robust and durable, as well as thin enough that it won’t damage objects on contact. In fact, it’s as soft as the silicone used in most soft robots.
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The gripper is unique because it uses the whole length of the tape as a gripping surface. The tape can also move to rotate objects or act as a conveyor belt. The gripper can hold a wide range of objects with different shapes and stiffness, from a rubber ball or a single tomato to a whole tomato vine or a lemon. Because the tape itself can act as a conveyor belt, the gripper can then deposit the objects it grasps into containers. Because the tape is flexible, it can also navigate the obstacles the gripper might encounter on the way to picking up an object.
Experiments showed that the gripper could easily lift large fruits such as fresh lemons and oranges. Next versions of the gripper could improve on the original by adding advanced sensors and AI-driven data analysis so that the gripper can operate autonomously.
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The research has been published in Science Advances.