Fully Passive Robotic Finger for Human-Inspired Adaptive Grasping in Environmental Constraints

This article presents an adaptive finger mechanism for grasping objects in an environmental constraint. The proposed finger is designed such that it can be easily installed to a parallel gripper, and hence, operated using a single linear actuation system. The parallel gripper equipped with the proposed finger mechanism features capabilities of self-adaptation to various object shapes and interaction with environmental constraints. Besides, based on the interaction capability with environments, robotic grasping strategies inspired by human grasping approaches such as adaptive pinching and scooping are achieved. In particular, two types of scooping approaches corresponding to the symmetric and asymmetric configurations of the gripper are introduced. In this regard, Hart's linkage mechanism coupled with a parallelogram is applied to the proposed finger mechanism to synthesize the vertical translation for finger compliance as well as the unique transition motion between the pinching and scooping poses of the fingertip. These two degrees of freedom are entirely passive and can adapt to unknown objects or environmental constraints. The operating principle, limitations, and design guidelines for the proposed finger mechanism are analyzed through kinematics and statics. The fully prototyped two-finger gripper is evaluated through several demonstration scenarios to verify human-inspired grasping with objects of arbitrary shapes in environmental constraints.