  While the grasping capability of robotic grippers has shown significant
development, the ability to manipulate objects within the hand is still
limited. One explanation for this limitation is the lack of controlled contact
variation between the grasped object and the gripper. For instance, human hands
have the ability to firmly grip object surfaces, as well as slide over object
faces, an aspect that aids the enhanced manipulation of objects within the hand
without losing contact. In this letter, we present a parametric,
origami-inspired thin surface capable of transitioning between a high friction
and a low friction state, suitable for implementation as an epidermis in
robotic fingers. A numerical analysis of the proposed surface based on its
design parameters, force analysis, and performance in in-hand manipulation
tasks is presented. Through the development of a simple two-fingered
two-degree-of-freedom gripper utilizing the proposed variable-friction surfaces
with different parameters, we experimentally demonstrate the improved
manipulation capabilities of the hand when compared to the same gripper without
changeable friction. Results show that the pattern density and valley gap are
the main parameters that effect the in-hand manipulation performance. The
origami-inspired thin surface with a higher pattern density generated a smaller
valley gap and smaller height change, producing a more stable improvement of
the manipulation capabilities of the hand.
