| Underactuation has been utilized in the design of robotic hands to increase robustness and adaptability, and decrease complexity and cost. Researchers have previously shown that underactuated hands can be adept at grasping a large range of object geometries, requiring only simple, open-loop control schemes. However, the dexterity of underactuated hands and their capabilities beyond grasping have not been thoroughly explored. This thesis investigates the system requirements for useful dexterous manipulation primitives and evaluates various design modifications that can enhance an underactuated hand's manipulation capabilities.;In-hand, precision manipulation was studied by modeling the hand-object system as a closed-chain or parallel mechanism. Constraint-based energy minimization was used to determine the achievable configurations of underactuated hands with compliant joints. Our work validated this for the planar and spatial manipulation cases in simulation and physical experiments, utilizing two-link underactuated fingers. The experimental evaluation produced meaningful object workspaces comparable to those measured in human trials. However, rolling and slip at contact were persistent problems under normal operating conditions, limiting the repeatability and stability of these motion primitives.;To address the repeatability and stability of in-hand manipulation with underactuated hands, we also explored the utility of caging, where the hand configuration does not necessarily fully constrain an object, but instead limits its pose to a bounded range. This methodology leverages the power-grasping capabilities of underactuated hands and provides a more robust strategy for continued, stable manipulation without requiring persistent contact conditions. Physical experiments were run for a range of object geometries and hand topologies to evaluate the achievable workspaces.;Our research enables underactuated hands to make adjustments to the object pose and correct for grasping errors. The strategies investigated in this thesis can be implemented without significant mechanical modifications to pre-existing underactuated hand designs, thereby maintaining their effectiveness at adaptive grasping. |
