Auxetic-structured parallel gripper with negative poisson's ratio characteristics

Parallel grippers are widely employed in industrial settings owing to their structural simplicity, precise control, and low cost. However, they often exhibit limited adaptability and low gripping efficiency when handling fragile or irregularly shaped objects. To enhance these capabilities, this study investigates the incorporation of negative Poisson’s ratio (NPR) structures, recognized for their auxetic behavior, into gripper design. Two NPR-based configurations, the re-entrant hexagonal honeycomb (RHH) and the double-auxetic honeycomb (DAH), were designed, fabricated using additive manufacturing, and systematically evaluated through experimental tests and finite element simulations. Compared to conventional solid grippers, the NPR-based designs significantly reduce the required normal force while achieving comparable or superior gripping performance. This makes them particularly suitable for grasping fragile, brittle, or irregular objects. The improvement arises from the auxetic effect: under compression, the structures contract laterally, conforming to the object’s shape and forming an enveloping grasp that increases contact area and enhances holding force via friction and geometric constraints. Notably, the DAH structure demonstrated better performance than the RHH, with maximum gripping efficiencies of 3.54 and 3.29, respectively. This advantage is attributed to the DAH’s more localized stress distribution near contact regions, stronger lateral contraction, greater structural stability, and more effective envelope formation. These findings underscore the potential of DAH-based NPR structures for enabling adaptive, stable, and efficient grasping in both soft robotics and industrial applications.