Internal force control with no object motion in compliant robotic grasps

The control of internal forces is one of the key issues in grasping. When the robotic hand is compliant, for instance with passive springs at the joints, and the number of controlled variables is low, as shown in recent works for underactuated hands, it is possible that the control of internal forces implies the motion of the manipulated object. This paper deals with this issue and studies the structural conditions for the control of internal forces which do not involve any motion of the grasped object. The analysis is constructive and a controller of internal forces is proposed. Note that guaranteeing zero motion of the object while controlling internal forces is paramount in robotic manipulation when the task requires large accuracy.