  Grasping unknown objects has been an active research topic for decades.
Approaches range from using various sensors (e.g. vision, tactile) to gain
information about the object, to building passively compliant hands that react
appropriately to contacts. In this paper, we focus on grasping unknown objects
using proprioception (the combination of joint position and torque sensing).
Our hypothesis is that proprioception alone can be the basis for versatile
performance, including multiple types of grasps for objects with multiple
shapes and sizes, and transitions between grasps. Using a
series-elastic-actuated gripper, we propose a method for performing stable
fingertip grasps for unknown objects with unknown contacts, formulated as
multi-input-multi-output (MIMO) control. We also show that the proprioceptive
gripper can perform enveloping grasps, as well as the transition from fingertip
grasps to enveloping grasps.
