A soft gripper with programmable effective length, tactile and curvature sensory feedback

Soft grippers based on fluidic elastomer actuators have the characteristics of gentle and adaptable grasping that is difficult to realize by rigid grippers. However, it remains challenging to implement a compact gripping device that has multiple bending configurations to exert appropriate force, and sensory capabilities to evaluate the grasping state. Here, we present a soft gripper with variable effective lengths (VELs) that is achieved by rapidly softening selective shape memory polymer sections (within 0.6 s) via a flexible heater. A vortex tube is used to jet cold airflow to accelerate the stiffening process (within 14 s). We show that the soft gripper can not only identify objects but also exert higher gripping force by setting appropriate length according to pneumatic-thermal hybrid actuation. We further propose a touch-reconfiguration-grasp strategy to showcase the synergy of VELs and sensory feedback. The gripper first touches the object under the fully softened state and evaluates the grasping condition based on the sensors' feedback, then reconfigures the bending length and grasps the object until successful. We envision that soft grippers with sensing ability and reconfigurable grasping configurations would be promising for future applications in unconstructed environments.