A novel variable stiffness soft gripper based on air-quicksand: design, analysis, and validation

Abstract This paper presents a novel variable stiffness soft gripper based on the principle of air-quicksand to enhance both the grasping stability and load-bearing capacity. The design, fabrication, and testing experiments of the soft grippers were performed. The soft finger is composed of a variable stiffness layer and a pneumatically driven layer with variable height chambers. The concept behind the variable stiffness layer lies in the fact that when the chamber is filled with air, it forms a suspended quicksand configuration through laminar flow and turbulence. This arrangement increases the spacing between sand particles, leading to reduced friction. Moreover, the stiffness and hardness of the soft finger can be controlled by adjusting the pressure. To improve the grasping stability, the variable height chambers were designed to provide power, which also increased the contact area. Experimental results demonstrate that the variable stiffness layer can be softened when in contact with fragile objects, thus protecting the surface without causing any damage. The stiffness increases to provide sufficient grasping force for holding objects firmly after the inflation is stopped. The exceptional performance exhibited by this gripper design holds significant potential for various applications, such as industrial sorting and fruit picking.