As engineering professor Mable Fok saw how the pole beans in her garden wrapped tightly around any objects nearby, she had an idea:

What if a robotic gripper could do the same thing?

“I did some research on twining plants and thought it was a good design from nature for us to explore," said Mable Fok , an associate professor at the University of Georgia and lead researcher of a robot that can wrap up an object.

As pole beans grow upward, the twining plant uses touch-sensitive shoots to coil itself around supports like ropes and rods. The UGA team designed a robot with a similar wrap-up grasping mechanism.

The robotic gripper, made from silicon, can get a hold of objects as small as 1 millimeter in diameter.

The study was published in the journal Optics Express .

The robot’s twining action is a simple one, requiring only a single pneumatic control. The UGA-developed device also offers an additional advancement over many existing robotics: an embedded sensor to provide critical real-time feedback.

“We have embedded a fiber optic sensor in the middle of the robot’s elastic spine that can sense the twining angle, the physical parameters of the target, and any external disturbances that might cause the target to come loose,” said Fok.

Measuring approximately three inches in length, the soft robotic gripper perhaps offers valuable applications in settings that have little operational space.

The robotic gripper may also support tasks that require a soft touch, according to the UGA team, like packaging agricultural products; performing surgeries, or handling research samples in fragile glass tubes.

In tests, the team showed how the spiral device effectively gripped traditionally tough-to-grip objects such as pencils and paintbrushes – even the thin wire of a straightened paperclip.

Next, the team plans to improve the automatic feedback control based on the readings of the fiber optic sensor.

In a short Q&A, via email, with Tech Briefs below, Fok reveals more about how the team wants to improve the design, and miniaturize it.

Tech Briefs: A pole bean seems like an unlikely source of inspiration for a robotic arm. Can you tell us more about that connection between a pole bean and an effective robotic arm/gripper, and what inspired you to give the arm pole-bean-like characteristics?

Prof. Mable Fok, UGA
Professor Mable Fok. (Image Credit: Andrew Davis Tucker/UGA)

Prof. Mable Fok: The uniqueness in a twining plant is that during its spiral movement around the target, the plant establishes discrete points of contacts, which create anchorage points to securely hold onto the target.

In a twining plant, a directional growth movement, known as Thigmotropism, governs how the plant twines onto the target, such that the growth rate on the side of the stem, which is being touched, is slower than the opposite side that is not being touched, making the stem grow spiral on the target.

In our design, a single-spiral air channel for pneumatic powering is used to mimic the directional growth movement in a twining plant, such that the soft robotic gripper can wrap around the target spirally.

We were trying a couple designs to build a compact gripper. Then, I remembered the pole bean that I accidentally got from my home’s garden and thought it could be a nice model, so we tried it.

Tech Briefs: How is your robotic gripper different than other robotic ones? Does it look different too, compared to “conventional” ideas of robotic grippers?

Prof. Mable Fok: Our robot’s twining action only requires a single pneumatic control, which greatly simplifies its operation and eliminates the need for complex coordination between multiple pneumatic controls. Since we use a unique twining motion, the soft robotic gripper works well in confined areas.

Tech Briefs: What kind of feedback is being offered from the fiber optic sensor?

Prof. Mable Fok: The embedded fiber optic sensor provides information regarding the angle of twining, the diameter of the target object, and any external perturbation.

Tech Briefs: What is the arm especially good at gripping, and in what applications do you see this arm being used most effectively?

Prof. Mable Fok: The spiral gripper is especially good at gripping elongated objects. Its applications span from agriculture, to medicine, and to research.

Tech Briefs: What’s next? What are you working on now with the robotic gripper?

Prof. Mable Fok: We want to improve the automatic feedback control based on the readings of the fiber optic sensor. We also want to explore miniaturizing the design to serve as the foundation of a biomedical robot.

What do you think? Share your questions and comments below.

In addition to Fok, the research team includes Mei Yang and Ning Liu, both Ph.D. candidates in engineering; Liam Paul Cooper, an undergraduate studying computer systems engineering; and Xianqiao Wang, an associate professor in the College of Engineering.