On the force capability of underactuated fingers

This paper studies the force capability of a particular class of underactuated fingers. Force capability is defined as the ability to create an external wrench onto a fixed object. The concept of the underactuation in robotic fingers, with fewer actuators than degrees of freedom (DOF) through the use of springs and the mechanical limits, allows the hand to adjust itself to an irregularly shaped object without complex control strategy and numerous sensors. However, in some configurations, the force distribution in an underactuated finger can degenerate. The finger can no longer apply forces on the object, leading in some cases to the ejection of the latter from the hand. This paper focuses on a 2-DOF finger and studies its ability to seize objects with a secure grasp.