  Robot arms that assist humans should be able to pick up, move, and release
everyday objects. Today's assistive robot arms use rigid grippers to pinch
items between fingers; while these rigid grippers are well suited for large and
heavy objects, they often struggle to grasp small, numerous, or delicate items
(such as foods). Soft grippers cover the opposite end of the spectrum; these
grippers use adhesives or change shape to wrap around small and irregular
items, but cannot exert the large forces needed to manipulate heavy objects. In
this paper we introduce RIgid-SOft (RISO) grippers that combine switchable soft
adhesives with standard rigid mechanisms to enable a diverse range of robotic
grasping. We develop RISO grippers by leveraging a novel class of soft
materials that change adhesion force in real-time through pneumatically
controlled shape and rigidity tuning. By mounting these soft adhesives on the
bottom of rigid fingers, we create a gripper that can interact with objects
using either purely rigid grasps (pinching the object) or purely soft grasps
(adhering to the object). This increased capability requires additional
decision making, and we therefore formulate a shared control approach that
partially automates the motion of the robot arm. In practice, this controller
aligns the RISO gripper while inferring which object the human wants to grasp
and how the human wants to grasp that item. Our user study demonstrates that
RISO grippers can pick up, move, and release household items from existing
datasets, and that the system performs grasps more successfully and efficiently
when sharing control between the human and robot. See videos here:
https://youtu.be/5uLUkBYcnwg
