A Gripper with Extreme Stiffness Anisotropy for High-Speed Handling of Fragile Foods

Abstract

Handling fragile objects at high speeds presents a significant challenge. To address this challenge, researchers explored hybrid grippers and grippers with adjustable stiffness. However, grippers exhibiting anisotropic stiffness have received little attention. This paper presents an extreme case of an anisotropic stiffness gripper designed for high-speed handling of delicate foods. The proposed gripper incorporates linear motors and low-friction linear guides. Its extremely low friction in the grasping direction ensures minimal grasping force (less than 0.1 N) and high compliance, enabling the secure handling of fragile objects. Simultaneously, its rigid structure provides sufficient stiffness in the translational direction, ensuring stability during high-speed motion. Leveraging anisotropic stiffness, the gripper achieves both gentle grasp and stable high-speed translation--two requirements that typically necessitate a trade-off. Theoretical analysis was conducted to determine the maximum permissible acceleration under two conditions: with and without stiffness anisotropy. Results indicate that stiffness anisotropy enables significantly higher acceleration during translational motion, thereby reducing task time. Pick-and-place experiments on a 3D printed object, delicate foods of a potato chip, a block of tofu, and a piece of dried seaweed validated theoretical findings and demonstrated the gripper's capability to handle fragile objects at high speeds effectively.