Engineers develop soft drone grippers inspired by climbing plants

HANGZHOU -- A team of Chinese engineers has developed a new class of biomimetic soft drone grippers that allow unmanned aerial vehicles (UAVs) to perform a variety of tasks, such as retrieving a key hanging from a tree branch or snatching branches from moving water.

Aerial transportation and manipulation extend the capabilities of UAVs, but the rigid grippers they use tend to be heavy, have a single grasping mode, and are limited in terms of the shape and size of the object that can be grasped.

Tendril plants are often characterized as having exceptional grapnels, possessing the remarkable ability to tightly clutch onto branches with their entangled, soft and grasping forms. Also, there is another category of climbing plants that have evolved with hook-like structures that enable them to scale the vertical surfaces of tall buildings.

Researchers from Zhejiang University drew inspiration from such climbing plants and designed two U-shaped, eccentric circular tube actuators. The U-shaped bending ability of these actuators allows UAVs to grasp objects by using a hook or a vine-like rope.

Based on these two types of actuators, researchers then proceeded to construct two types of soft grippers, thereby forming self-contained systems that can be directly driven by voltage.

The gripper inspired by soft tendril climbers is designed for delicate grasping, while the one inspired by hook climbers can be used for tasks requiring strong grasping, according to a study published as a cover story in the latest edition of the journal Science Advances.

The load capacity for a single actuator with hook structures is about 29 percent more compared to one without such a hook, and it can grasp a maximum weight of approximately 450 grams, according to the study.

This type of gripper mounted on a drone demonstrated its capabilities by successfully grasping common household items like plastic bottles, glass goblets, clamps and ceramic ornaments.

In an outdoor experiment, a drone flew towards a key suspended from a tree limb. Its self-adaptive gripper passed through tree limbs and then managed to firmly grasp the key via a voltage that was applied to the resistance wires.

This UAV grasping solution can be useful in environmental protection, where it can be deployed for tasks such as gathering trash in the wild and removing garbage from rivers and lakes. In freshwater ecosystems, manual collection currently remains the main method of garbage cleanup, which means it is labor-intensive.

In another outdoor experiment, the research team used a UAV to salvage a branch suspended in a lake. A drone flew to a specific lake area and immersed the gripper in the lake. The U-shaped elongated gripper then demonstrated its effectiveness by successfully hooking the branch, while its self-contained system steadily supplied gas underwater, resulting in a secure and firm grasp on the object. Finally, the drone ascended and returned to shore.

Unlike rigid grippers, the soft and adaptable gripper can absorb vibrations transmitted by UAVs and also allows an object to rotate or move within the gripper.

Outdoor applications have highlighted the unique advantages of the soft grippers across a spectrum of challenging environments. Such grippers can operate effectively even in cases of low positioning accuracy, reducing the need for complex planning concerning grasping execution, according to the researchers.

The researchers added that soft grippers have proven that they can be used for efficient UAV transportation by winding around or hooking objects with manual assistance in challenging transportation terrain, such as steep mountain slopes.