Prosthetic hands are a means for people with upper limb amputation to perform activities of daily living without external assistance. The goal of prosthetic hand design is to make dextrous and versatile hands at a low cost. To this end, the human hand serves as an inspiration for the design and development of prosthetic hands. This is primarily because the human hand possesses unmatched dexterity and versatility obtained through millions of years of evolution. This is despite the hand having a complex anatomy and physiology. The sophisticated control of the hand is attributed to the central nervous system (CNS) which controls a large number of degrees of freedom in the hand through a reduced set of variables. This reduced set of variables is known as synergy and it is the basis for underactuation employed in the design and control of robotic hands. To extract postural synergy, a kinematic grasp dataset involving the human participants is collected. This dataset is used to obtain the design parameters of various components of the prosthetic hand as well as validate the design to ensure anthropomorphism. A prosthetic hand can be comfortably used by a patient only if the device is lightweight, affordable, and can perform activities of daily living. Hence, a prosthetic hand with a minimalistic design is proposed in this work.
The hand is designed to have hybrid fingers consisting of linkage-based fingers that are controlled by tendons. This novel architecture of the fingers provides improved anthropomorphic behaviour over conventional linkage-based fingers. Further, the fingers are oriented at an inclination on the palmar surface. This orientation of the fingers ensures that the hand has the functionality provided by the abduction/adduction motion at the metacarpophalangeal (MCP) joint with three degrees of freedom fingers. The thumb and little finger are mounted on hinged platforms capable of providing in-plane rotation for enhanced dexterity. Further, all the motions of the thumb and little finger are coupled individually using differential mechanisms to provide anthropomorphic as well as anthropometric grasping capabilities to the designed prosthetic hand. Finally, a synergy-based motion transmission mechanism is designed for effective force transfer from the three input motors to all the active joints.