A methodology for setting grasping force for picking up an object with unknown weight, friction, and stiffness

A methodology for setting the reference value of a grasping force when a multi-finger robotic hand grasps and lifts up an object without knowing its characteristic weight, coefficient of static friction, and stiffness was devised. The grasping force must be set to avoid dropping or deforming the object. To fulfill this requirement, the methodology measures object characteristics by detecting the moment of deformation or slipping according to the deflection of a mechanical passive element. The reference value of grasping force is set according to an upper limit to avoid crushing and a lower limit for lifting up the object calculated from the object´s above-mentioned characteristics. The degree of the accuracy of object characteristic measurements was evaluated through experiments using an actual human-mimetic hand-arm system. Finally we validated that the system can pick up objects with the grasping force set by our methodology.