Functionally Divided Manipulation Synergy for Controlling Multi-fingered Hands

Synergy provides a practical approach for expressing various postures of a multi-fingered hand. However, a conventional synergy defined for reproducing grasping postures cannot perform in-hand manipulation, e.g., tasks that involve simultaneously grasping and manipulating an object. Locking the position of particular fingers of a multi-fingered hand is essential for in-hand manipulation tasks either to hold an object or to fix unnecessary fingers. When using conventional synergy based control to manipulate an object, which requires locking some fingers, the coordination of joints is heavily restricted, decreasing the dexterity of the hand. We propose a functionally divided manipulation synergy (FDMS) method, which provides a synergy-based control to achieves both dimensionality reduction and in-hand manipulation. In FDMS, first, we define the function of each finger of the hand as either "manipulation" or "fixed." Then, we apply synergy control only to the fingers having the manipulation function, so that dexterous manipulations can be realized with a few control inputs. Furthermore, we propose the Synergy Switching Framework as a method for applying a finely defined FDMS to sequential task changes. The effectiveness of our method is experimentally verified.