| Description |
Both the human hand and current 1-DOF prosthetic hands, such as the Ottobock SensorHand Speed hand, prevent slip while grasping objects by increasing the grip force. The question is what is the appropriate amount of grip force to apply to the object to recover from slip. A slow response with insufficient force results with dropping the object. However, excessive force may damage some objects. The prosthesis has limited information about the grasped object except for the grip and load forces. The proposed approach is to have a prosthetic hand control slip similar to a human hand by imitating how a human solves the problem in a worst-case scenario: stopping the slip of a brittle object with minimal forces. The human has full knowledge of the object's properties, so it is presumed that the human implements a near-optimal solution to recover from slip. Observations were made to examine how the human hand recovers from slip of a fragile object depending on the surface material, mass, and breaking strength of the object. Results suggest that a prosthetic hand be designed to hold an object with sufficient grip force to retain a secure grasp and respond to slip by increasing the grip force by 1.5 times within 75 ms to restore a secure grasp. |
