  Realizing high-performance soft robotic grippers is challenging because of
the inherent limitations of the soft actuators and artificial muscles that
drive them, including low force output, small actuation range, and poor
compactness. Despite advances in this area, realizing compact soft grippers
with high dexterity and force output is still challenging. This paper explores
twisted string actuators (TSAs) to drive a soft robotic gripper. TSAs have been
used in numerous robotic applications, but their inclusion in soft robots has
been limited. The proposed design of the gripper was inspired by the human
hand. Tunable stiffness was implemented in the fingers with antagonistic TSAs.
The fingers' bending angles, actuation speed, blocked force output, and
stiffness tuning were experimentally characterized. The gripper achieved a
score of 6 on the Kapandji test and recreated 31 of the 33 grasps of the Feix
GRASP taxonomy. It exhibited a maximum grasping force of 72 N, which was almost
13 times its own weight. A comparison study revealed that the proposed gripper
exhibited equivalent or superior performance compared to other similar soft
grippers.
