Development of an underactuated hand prosthesis with compliant control

Abstract

The main subjects of this thesis are the mechanical design and control of a new hand prosthesis prototype: the UT Hand I. The functionality of modern hand prostheses is mainly limited by the size and weight of their actuators. The UT Hand I features a minimal actuation system, where all finger joints are connected to a single electric motor. The ability to control these joints separately is preserved by miniature locking mechanisms which fit inside the fingers and palm. Combined with a separately movable thumb, the hand allows the user to perform various grasps relevant to daily living. To provide the user and the control system with feedback during grasping, the hand contains position sensors in the finger joints; additionally, each fingertip contains a set of four force sensors coated in rubber. The control of the UT Hand I is based on ‘myoelectric’ signals: electrical impulses produced by the activation of the user’s remaining forearm muscles. A special interface provides a selection of grasp types for precision and power grasping; the user can control which of these grasps to use (and when) by flexing the appropriate muscles. A control system has been developed to automatically close the fingers and thumb around an object, and hold it with a force controllable by the user. The system also controls the energy applied by the motors, in order to maintain a stable grasp and ensure safe interaction with objects and people at all times. The completed UT Hand I system demonstrates several innovative mechanical design and control techniques, which improve the functionality and controllability of modern myoelectric hand prostheses.