PEGrip: A Plant-Tendril-Inspired Passive Entanglement Gripper Enabling Fail-Safe Grasping

Soft robotics, including soft grippers and manipulators, are increasingly required to function more adaptively and securely in unknown environments. However, conventional soft pneumatic grippers often grasp and hold objects via the active bending of multiple fingers, making it challenging to grip and hold, for example, spiny objects safely because of the potential damage to the pneumatic chambers. In this letter, inspired by the entanglement behavior of plant tendrils, we propose a soft, pneumatic, fail-safe gripper. The fail-safe property is guaranteed by two mechanisms, the passive entanglement and the redundant contacts. Specifically, the gripper exploits an array of tentacle fingers that actively extend and passively entangle for entanglement grasping. To understand the working principle, we studied the entanglement behavior of a single tentacle finger by both analytical modeling and finite element method simulation. We also characterized the griping capability of this gripper in a series of different grasping experiments. The gripper was demonstrated to be capable of grasping a range of different objects, from artificial ones with simple shapes to real-world targets with complex shapes. We finally showcased the fail-safe property of this gripper in a pick-and-lift task by comparing the performance of this gripper with that of a conventional gripper when the two grippers are manually damaged. This work paves the way for the development of soft pneumatic grippers with fail-safe and reliable grasping.