Variable stiffness soft pneumatic grippers augmented with active vacuum adhesion

Soft pneumatic grippers (SPGs), made of highly stretchable elastomer materials with internal fluidic channels, are a popular soft robotic gripping technology, and have been configured as soft bending fingers for passively compliant grasping applications. It is challenging, however, for current SPGs to grip both flat, concave, and convex surfaces. Controllable adhesion augmented SPGs are promising solutions. We aim to develop a composite gripper structure that could enable SPGs with the capability to lift flat, concave, and convex surfaces using pneumatic inputs only. To this end, we present PneuIVAVS, a layer-jamming induced active vacuum adhesion (VA) augmented and variable stiffness (VS) fiber-reinforced SPG. This integrated PneuIVAVS design has enabled the gripper to generate a VA force without the requirement that all suction units should work. Also, a VA force analytical model and a shape-locking model of the PneuIVAVS design were developed and experimentally validated. In addition, the PneuIVAVS gripper presented good performance on gripping both flat, concave and convex objects with a range of contacting areas. According to the load capacity test, the gripper could grasp a maximum of approximately 470 g, 683 g, and 268 g when handling flat, concave, and convex surfaces respectively. Besides, the gripper could grasp curved surfaces with a minimum radius of curvature between 30 and 40 mm. The PneuIVAVS concept, design, and results in this work have potential to promote the applications of SPGs and VA grippers in various material handling and robotics tasks.