  Soft grippers are receiving growing attention due to their compliance-based
interactive safety and dexterity. Hybrid gripper (soft actuators enhanced by
rigid constraints) is a new trend in soft gripper design. With right structural
components actuated by soft actuators, they could achieve excellent grasping
adaptability and payload, while also being easy to model and control with
conventional kinematics. However, existing works were mostly focused on
achieving superior payload and perception with simple planar workspaces,
resulting in far less dexterity compared with conventional grippers. In this
work, we took inspiration from the human Metacarpophalangeal (MCP) joint and
proposed a new hybrid gripper design with 8 independent muscles. It was shown
that adding the MCP complexity was critical in enabling a range of novel
features in the hybrid gripper, including in-hand manipulation, lateral passive
compliance, as well as new control modes. A prototype gripper was fabricated
and tested on our proprietary dual-arm robot platform with vision guided
grasping. With very lightweight pneumatic bellows soft actuators, the gripper
could grasp objects over 25 times its own weight with lateral compliance. Using
the dual-arm platform, highly anthropomorphic dexterous manipulations were
demonstrated using two hybrid grippers, from Tug-of-war on a rigid rod, to
passing a soft towel between two grippers using in-hand manipulation. Matching
with the novel features and performance specifications of the proposed hybrid
gripper, the underlying modeling, actuation, control, and experimental
validation details were also presented, offering a promising approach to
achieving enhanced dexterity, strength, and compliance in robotic grippers.
