Unspooling measuring tape to see how far it would extend before bending is a game that plenty of people played as kids and possibly even later in life. However, this activity served as motivation for engineers at the University of California, San Diego, who thought that measuring tape might make a fantastic material for a robotic gripper. The findings were published in Science Advances on April 9th, 2025.
The gripper is comprised of two spools each made from two rolls of measuring tape bound together, and of four motors to direct its motions. Image Credit: University of California San Diego
The grippers’ extremities are soft enough to grab fragile fruits and vegetables, making them ideal for applications in agriculture, according to the researchers. The devices are also inexpensive and safe for humans.
The team named their robot GRIP-tape, an acronym for Grasping and Rolling In-Plane.
Building the ideal robotic gripper is still a work in progress. Existing expandable grippers are bulky because they require additional components to allow grasping appendages to grow. The gripper, designed by the UC San Diego team, solves this challenge.
This is due to the tape’s durability and flexibility, which allow it to be stored in a tiny container when retracted and extended to a long distance. After a series of trial and error, the engineers discovered that the optimal gripper configuration is two tapes bonded together with adhesive.
We like to look for non-traditional, non-intuitive robot mechanisms. The tape measure is such a wonderful structure because of its combined softness and stiffness together.
Nick Gravish, Study Senior Author and Faculty Member, Department of Mechanical and Aerospace Engineering, University of California San Diego
The gripper contains two “fingers,” each comprised of two spools linked together with measuring tape. Each spool is coiled up compactly, with only a small section projecting out in a triangle shape to form a finger. Four motors individually control these triangle portions, governing the finger’s movement.
Each finger may move independently. Triangle parts can be lengthened to reach farther away objects. They can also retract to bring objects closer to the robot arm, to which the gripper is attached.
The researchers had previously experimented with measuring tape as part of a National Science Foundation grant to examine soft materials that could bend while maintaining their shape.
The measuring tape is elastic, which means one can bend it in any direction, and it will return to its original position. It is also made of steel, which is strong and durable and thin enough not to damage objects while in contact. It is as soft as the silicone found in most soft robots.
The gripper is unique in that it utilizes the entire length of the tape as a gripping surface. The tape can also be used to spin things or as a conveyor belt. The gripper can hold objects of different shapes and stiffness, including a rubber ball, a single tomato, a full tomato vine, and a lemon.
Since the tape can function as a conveyor belt, the gripper can then place the objects it grasps in containers. As the tape is flexible, it can overcome any barriers that the gripper may encounter while picking up an object.
Experiments revealed that the gripper could effortlessly lift large fruits, such as fresh lemons and oranges.
The subsequent versions of the gripper could improve on the original by including improved sensors and AI-driven data analysis, allowing the gripper to work autonomously.
The National Science Foundation provided partial funding for this study.
A New Robotic Gripper Based on Measuring Tape is Sizing Up Fruit and Veggie Picking
Video Credit: University of California San Diego