A Helical Bistable Soft Gripper Enable by Pneumatic Actuation

There are many instances of helical mechanisms that are used to efficiently grasp different objects with various shapes and sizes in nature. Inspired by the helical grasping in the nature, we proposed a helical bistable soft gripper with high load capacity and energy saving. An off-the-shelf bistable steel shell (BSS) as the stiff element was inserted into a 3D printing soft helical exoskeleton to achieve coiling around and holding the objects without energy consumption. Two air pouches were designed as the actuator to control the transition between the two stable states. To facilitate gripper design, a simplified model of the gripper was conducted, and the geo- metric parameters of the gripper are listed in a table for refer- ence. The transition pressures between the two stable states were experimentally characterized. Moreover, we conduct ex- periments to demonstrate the capability of the gripper in two working modes. The gripper exhibits coiling diameters ranging between 40 mm and 60 mm and is successfully attached to var- ious slender objects of different geometries with a maximum holding force of 92.67 N (up to 135.1 times of its mass) in hang- ing mode. Finally, the gripper was integrated into a robot arm and successfully grasped different objects, and the maximum grasping weight is 221.6 g in the grasping mode.