Design and Validation of a Soft Self-Centering Gripper for Delicate Object Handling
Xiaoqian Zhang, Mario Baggetta, Cristina Piazza, Giovanni Berselli
AI summary
Problem
Conventional rigid or purely passive soft grippers struggle to balance high gripping force with low localized stress, often causing bruising or losing grip stability on delicate, irregular produce in unstructured environments.
Approach
The authors developed a three-finger soft gripper that combines linear finger sliding for self-centering with active curvature pre-shaping via auxetic actuators to match object geometry before clamping.
Key results
- Simulations show pre-shaping yields more uniform contact pressure and lower peak stress than passive compliance
- Functional prototype fabricated via additive manufacturing
- Experimental pull-out tests confirm increased grasp stability and resistance
- Design successfully decouples sliding and bending actuation to prevent frictional coupling
Why it matters
Provides a practical, damage-free grasping solution for agricultural robots handling delicate and irregular fruits in unstructured harvesting environments.
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 gen- erate localized load concentrations and require high positioning accuracy, limiting their effectiveness in unstructured environ- ments. 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.