A two-fingered underactuated anthropomorphic manipulator based on human precision manipulation motions

Abstract

While designing robot hands based on grasping data is more common, fewer previous works have used details of human manipulation kinematics to improve robot hand design. The current work involves an underactuated, tendon driven, anthropomorphic manipulator with two flexor tendons and an abduction-adduction tendon, and describes its design based on experimental human precision manipulation data. Link lengths, joint axis alignment, and moment arms were derived from human subject data and values in the literature. The spring ratios, determining the torque relationships between joints, were then selected to maximize the achievable manipulation workspace from the human trial without requiring large forces, which are likely to lead to instability and object ejection. This is done by minimizing the stored spring energy in the robotic fingers across the range of precision manipulation workspace positions achieved by a representative human subject. After fabricating the hand, the energy characteristics of the resulting prototype are analyzed, and the robotic workspace is compared against the original human one. Despite only having three actuators, the hand is able to manipulate the test object within a 2.7 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> workspace volume, compared to an average human workspace of 5.4 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> for the same object. Future work could include adding antagonist actuators to achieve a larger motion range along the palmar-dorsal axis, which is currently the most limited axis of motion in comparison to the original human workspace.