Scale-dependent grasp-a case study

This paper discusses scale-dependent grasp. Human beings unconsciously change their grasp strategy according to the size of objects, even though those objects have similar geometry. We first observe the grasping strategy of the human hand in wrapping around a cylindrical object placed on a table. We show that the human grasp planning can be roughly classified into three patterns according to the object´s size. For a large cylindrical object, the human hand wraps around it directly without any regrasping process. As the diameter of the object decreases, a human begins to slip the object along the finger, so that the object can finally make contact with the palm. For a further smaller diameter, a human first picks it up by his/her finger tips and then makes a transition from a finger tip to a wrapping grasp. We also extract the essential motions of human grasping so that we can implement them in multifingered robot hands