Mapping human hand fingertips motion to an anthropomorphic robotic hand

The mapping of the human intention to a dexterous anthropomorphic robotic hand is still an open issue among researchers. The complexity behind this problems comes mainly from three factors: the kinematics differences between the users and the robotic hand(s); the differences in size and motion capabilities among different users hands; and the high number of degrees of freedom present in an anthropomorphic hand. In this work, we present a procedure for the determination of a linear transformation capable to interface the user and the robot kinematics and therefore to allow a precise and natural control of the mechanical device. The main assumption that we make is that different human hand kinematics differ -with a good approximation- for a scaling factor only, whereas the proportions between the phalanges lengths and the relative orientation of the fingers are kept almost constant in healthy people [1]. We also assume that, being the considered robotic hand highly anthropomorphic, this condition holds also between the user and the robotic hand. In addition, while for a robotic hand the definition of a reference frame fixed to the palm is a free choice, for the human hand tracked with some external system it is completely software dependent. Therefore additional rotational and translational corrective terms have to be introduced to compensate for the different placement of the palm reference frame with respect to the fingers. We have applied this approach to control the UB-Hand IV using a commercial device called Leap Motion, able to track with a good accuracy the pose of the palm and the positions of the key points of the human hand, i.e. the end points of the hand bones [2].