Rapidly Tunable Stiffness Soft Gripper for Multifunctional Grasping

The flexible gripper exhibits limited load capacity while possessing dexterity and adaptability to complex environments. Conversely, the thermally-driven variable stiffness gripper boasts high load capacity but suffers from slow response times. This study presents a multifunctional flexible gripper characterized by rapid response and high load capacity, achieved through a combination of thermally responsive variable stiffness fingers and a jet-cooling system. The thermally responsive variable stiffness fingers are composed of a layered material comprising liquid metal particles and shape memory polymer composites, with stiffness ranging from 3.56 MPa to 4356 MPa, spanning three orders of magnitude. The maximum load capacity reaches $\sim$ 13 N (single finger at 15 mm deflection) with a maximum bending angle of $\sim 82^{\circ }$ and a rapid stiffening speed of $\sim$ 2 s. The gripper, consisting of three fingers, can grasp objects up to $\sim$ 54 times finger weight, including oranges, empty plastic cups, and other deformable objects. We discuss the thermal-stiffness response characteristics and mechanical properties and demonstrate the variable stiffness gripper's ability to grasp targets of different sizes and masses in various initial orientations. This work shows the potential applications of flexible manipulators in the rapid, damage-free grasping domain.