Multimaterial Soft Gripper Design With Dual-Mode Pinches for Grasping in Confined Spaces

Pinch is an indispensable grasping primitive of human hands and traditional rigid grippers, eminently suitable for handling small-sized and dense objects, but it is rather under-researched in the context of soft robotics. In this article, with the aim of combining the inherent advantages of soft materials and the pinch grasp primitive to enable delicate object manipulation in confined spaces without causing damage, we present a compliant, compact, and powerful gripper capable of pinching small objects in two deformation modes: abduction and adduction. The design is enabled by a density-based multimaterial topology optimization approach that automatically seeks the optimal tradeoff between the expected deformation and gripping force. The optimized design mainly contains two materials, and is fabricated with a customized voxel 3-D printing strategy by controlling the local mixing ratio of the soft and hard inks. The simulation and experiments show that the obtained multimaterial design remarkably outperforms the single material design in terms of deformation and payload. We demonstrate that an array of the designed grippers can work collectively to grasp dense objects in a single process. Further, the gripper can work as an end effector of a hyper-redundant robot arm that navigates a narrow space, and fetch small objects therein with compliance and safety.