Stiffness-Tunable Soft Gripper with Soft-Rigid Hybrid Actuation for Versatile Manipulations

Highly flexible and environmentally adaptive soft robots have received considerable attention. There remains a demand for soft robots to realize the stiffness modulation and variable workspace for robust and versatile manipulations. This article presents a compact soft gripper with a polylactic acid-based variable stiffness module (VSM) and a rigid retractable mechanism to achieve soft-rigid hybrid actuation. The soft gripper can enhance its stiffness by 18-fold without sacrificing flexibility due to the VSM. A heating circuit is designed to divide the VSM into three regions. Each region can be activated separately for varying flexible segments to amplify the dexterity. Meanwhile, the water-cooling system accelerates the heat exchange, thus reducing the cooling time from ∼400 to 39 s. The rigid retractable mechanism can adjust the initial layout of the gripper to expand the workspace and perform manipulation by opening and closing fingers. The soft finger combined with stiffness tunability can maintain its deformation after being stiffened to realize morphing. Therefore, it can efficiently perform a grasp with a high load and avoid repeated heating and cooling, especially for items with a similar shape. The performance of the gripper is further validated by measuring the grasping force and grasping demonstration with various objects, showing its robustness and dexterity in versatile tasks.