Mathematical Modelling of a Four-Fingered Metamorphic Anthropomorphic Hand on Precision Grasp

For a metamorphic robotic hand with a foldable palm, its finger operation planes change with palm configurations. Although this reconfigurable design can enhance the grasp flexibility, manipulation workspace and application adaptability, the hand's grasp stability cannot be guaranteed when the palm reconfigures. Especially for the four-fingered metamorphic hand performing precision grasps in anthropomorphic postures, improper control of the palm configurations can result in unsuccessful grasps, which may even lead to hand damage. This paper first displays the workspace of the four-fingered anthropomorphic hand for generating precision grasp gestures. Based on it, force-closure/-balance analyses are performed, deriving the effective precision grasp workspace for typical anthropomorphic postures classified by built mathematical definition. Grasp levels are further discussed by introducing an evaluation method which considers the minimum friction coefficient (MFC) as the quality metric. The proposed scheme gives a way to depict the grasp performance of every robotic hand configuration, without considering specific objects that are to be grasped. Dynamic changes in postures' grasp performance with palm configurations are exhibited in the end.