Chinese engineers develop plant-inspired soft drone grippers for delicate tasks

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

Existing UAV grippers face persistent challenges in dynamically grab objects. Researchers from Zhejiang University drew inspiration from climbing plants and designed two U-shaped, eccentric circular tube actuators. The U-shaped bending ability of these actuators allows UAVs to grasp objects using a hook or a vine-like rope, proposing a class of plant-inspired grippers that are soft and self-adaptive enough to achieve powerful UAV manipulation. 

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 grips, according to a study published as a cover story in the latest edition of the journal Science Advances.

These improvements will allow UAVs to better interact with both delicate and heavy objects. It will also enable UAVs to perform well in multiple environments, paving the way for UAVs well-suited to environmental protection tasks such as removing garbage from rivers.

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

Powerful UAV manipulation

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 and the remarkable ability to tightly clutch branches with their entangled, soft and grasping forms. There is also another category of climbing plants that have evolved with hook-like structures that enable them to scale the vertical surfaces of tall buildings.

Using these two U-shaped, eccentric circular tube actuators as inspiration, Chinese researchers constructed two types of soft grippers, forming self-contained systems directly driven by voltage.

The load capacity of a single actuator with hook structures is about 29 percent more compared to one without, 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 everyday household items like plastic bottles, glass goblets, clamps and ceramic ornaments.

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

This UAV grasping solution can be useful in environmental protection, where it can used for tasks such as gathering trash in the wild and removing garbage from rivers and lakes. In freshwater ecosystems, manual collection remains the primary method of garbage cleanup, making it 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 lowered the gripper into 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, a soft and adaptable gripper can absorb vibrations transmitted by UAVs and allows an object to rotate or move within the gripper.

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

(With input from Xinhua)