Design and Validation of a Soft Self-Centering Gripper for Delicate Object Handling

Abstract

Harvesting, gripping, and handling of fruit and vegetables require end-effectors that ensure grip stability while, at the same time, minimizing surface damage and bruising. Conventional rigid or partially compliant solutions often generate localized load concentrations and require high positioning accuracy, limiting their effectiveness in unstructured environments. This work presents a novel three-finger gripper with a self-centering closing mechanism and soft fingers. The system operates in two stages: first, the fingers slide (FS) along linear guides driven by a dedicated motor to adapt to the object size; second, a separate motor actuates the finger closure to establish the grasp. The finger design is inspired by the handed-shearing auxetic (HSA) actuator, enabling controlled pre-shaping (PS) by adapting to the object geometry. The proposed design was first validated through finite element simulations, comparing pre-shaping (PS) against passive compliance (PC) under matched load conditions. Results demonstrate that PS significantly improves pressure uniformity and grasp stability. A fully functional prototype was then fabricated via additive manufacturing.