  In this paper, we propose a single-actuator gripper that can lift thin
objects lying on a flat surface, in addition to the ability as a standard
parallel gripper. The key is a crawler on the fingertip, which is underactuated
together with other finger joints and switched with a passive and spring-loaded
mechanism. While the idea of crawling finger is not a new one, this paper
contributes to realize the crawling without additional motor. The gripper can
passively change the mode from the parallel approach mode to the pull-in mode,
then finally to the power grasp mode, according to the grasping state. To
optimize the highly underactuated system, we take a combination of black-box
optimization and physics simulation of the whole grasp process. We show that
this simulation-based approach can effectively consider the precontact motion,
in-hand manipulation, power grasp stability, and even failure mode, which is
difficult for the static-equilibrium-analysis-based approaches. In the last
part of the paper, we demonstrate that a prototype gripper with the proposed
structure and design parameters optimized under the proposed process
successfully power-grasped a thin sheet, a softcover book, and a cylinder lying
on a flat surface.
