Soft-rigid coupling grippers: Collaboration strategies and integrated fabrication methods

Continuously increasing applications of robot technologies in unstructured environments put higher requirements on the robotic grippers' performance, such as interaction capability, output force range, and controllability. However, currently, it is hard for either rigid or soft grippers to meet these requirements, as single soft or rigid structures alone are difficult to effectively overcome/alleviate their inherent defects, e.g., low compliance of rigid structures and low output force of soft structures. To deal with these difficulties, soft-rigid coupling grippers, or hybrid grippers are proposed. Technically, the soft-rigid coupling is a promising design that combines soft and rigid structures, in order to exploit their respective advantages, such as the strength of rigid structures and compliance of soft structures, in the same set of the gripper system. For the first time, herein, this paper systematically discusses the collaboration strategies of the existing hybrid robotic grippers, by classifying them as Rigid-active-soft-passive, Rigid-passive-soft-active, and Rigid-active-soft-active. At the same time, we introduce the integrated fabrication methods of hybrid grippers, through which the soft and rigid structures with great stiffness and property differences can be coupled together to construct a stable system. Also, possible performance improvements on soft-rigid coupling design for gripper systems are discussed.