Anthropomorphic Dexterous Prosthetic Hand: Mechanical Design

Anthropomorphic Dexterous Prosthetic Hand: Mechanical Design ¨ Atasoy A., C¸otur Y., Toptas¸ E., Kuchimov S., Kaplano˘glu E., Takka S. and Ozkan M.

Abstract— Dexterity of a prosthetic hand is determined by its grasping and manipulation capabilities. Dexterity combined with anthropomorphic structure increases functionality as well as social acceptance. To achieve this the proposed mechanical design incorporates muscle, tendon and joint structures with a main intension to imitate human hand anatomy and functionality as much as possible.

like structure. Tunnels on both palmar and dorsal side of the designed finger keep the tendons close to phalanges, metacarpals and carpus which also prevent tendons from bowstringing and provide bio-mechanically efficient force transmissions.

I. INTRODUCTION Bones, muscles, tendons and joints are the main mechanical structures of the hand. The bone which is the main solid structure of the hand gives a body to hand posture. Ligament is connective tissue between bones keeping them together and constraining their movements whereas a tendon transmits force from muscle to bone.

Fig. 2: Anthrophomorphic finger design FDP and FDS tendons are imitated by means of cable ties to get the mechanically similar properties for their elasticity and strength features. The main role of the tendon is to transmit actuator generated force towards the acting point which is known as insertion point, and defined according to hand anatomy. III. ANALYSIS AND DISCUSSIONS

Fig. 1: Structures of human hand and its mechanical design Current hand prosthesis studies are focused on innovative solutions in grasping and posture capabilities[1-2]. These prosthesis however are based on rigid palm, have limited number of flexion-extension, and lack abduction-adduction.

Range of flexion-extension and abduction-adduction of DIP, PIP, MCP and CMC joints of digits and IP, MCP, CMC of thumb are constrained as shown in Table 1. Anatomic composition of thumb is unique than other digits. It has a containing only middle phalange and CMC joint has greater degree of freedom with wide range of motion. By achieving anatomically similar range of motion for all joints, possibility of producing human-like digit flexion, extension, abduction and adduction increases. TABLE I: RANGE OF MOTION JOINTS

II. DESIGN OF HAND The hand and wrist has 27 distinct bones; 14 phalanges, 5 metacarpals and 8 carpals. In the proposed design each phalanges and metacarpals designed in CAD and scaled according to the measured dimensions obtained from the CT data of a human hand. The proximal end of prosthetic hand comprised 8 fused carpals. Curvature structures of bone ends designed to obtain a bio-mechanically efficient fulcrum. Anatomically human hand joints provide mechanical support and constraints also incorporated in our design. In this design, moving parts are coupled by means of loose cylindrical for DIP, PIP and CMC and spherical for MCP and CMC joints as shown in Figure 1. The palmar side of finger has a ligamentous system comprising pulleys and synovial sheaths that form a tunnel *This work is supported by TUBITAK (113E158). *Patent pending.

Joints DIP Digit PIP MCP IP Thumb MCP CMC

Flexion / Extension Anatomic[3] Design 0 / 90 -20 / 110 0 / 100 0 / 115 -30 / 90 -35 / 120 0 / 80 -20 / 110 -10 / 55 0 / 90 -15 / 20 75

Abduction / Adduction Anatomic Design -20 / 20 -20/20 70 ROM 90 ROM

R EFERENCES [1] [1] Belter, J. T., Segil, J. L., Dollar, A. M., and Weir, R. F. (2013). Mechanical design and performance specifications of anthropomorphic prosthetic hands: a review. J. Rehabil. Res. Dev. 50, 599617. doi:10.1682/JRRD.2011.10.0188 [2] Zhe Xu, Kumar V., Matsuoka Y., and Todorov E., Design of an anthropomorphic robotic finger system with biomimetic artificial joints, Biomedical Robotics and Biomechatronics (BioRob), 2012 4th IEEE RAS & EMBS International Conference on, pp.568,574, 2012. [3] Whitney Lowe, Orthopedic Assessment in Massage Therapy, ISBN13: 978-0966119633, Daviau-Scott, 1st Edition, 2006.