Fabric-based star soft robotic gripper

Soft pneumatic gripping strategies are often based on pressurized actuation of structures made of soft elastomeric materials, which limits designs in terms of size, weight, achievable forces, and ease of fabrication. On the other hand, fabric-based inflatable structures offer high stiffness-to-weight ratio solutions for soft robotics, but their actuation has been little explored. Here we present a new class of pneumatic soft grippers that exploits the in-plane over-curvature effect of inextensible fabric flat balloons upon inflation. Our gripper has a star shape that contracts radially under pressure producing a gripping force on the object whose intensity can be modulated by the pressure input. We first focus on the kinematics and mechanics of a single V-shaped actuator through experiments, finite element simulations, and analytical models. We then leverage these results to predict the mechanical response of the entire star, optimize its geometry, and maximize contraction and stiffness. We demonstrate that the gripping force can be increased by stacking multiple stars in a rigid frame. We expect that the flexibility, robustness, scalability and ease of fabrication of our methodology will lead to a new generation of lighter and larger actuators capable of developing higher forces and moving delicate and irregularly shaped objects while maintaining reasonable complexity.