Robotic Finger Actuated with Shape Memory Alloy Tendon NICU-GEORGE BIZDOACA, ILIE DIACONU, MARIUS C. NICULESCU, ELVIRA BIZDOACA, SONIA DEGERATU, DANIELA PANA, CRISTINA PANA Department of Automatics University of Craiova 5 Tehnicii Street, Craiova, 1100 ROMANIA Abstract: - In the present article is explored the kinematics and statics of shape memory alloy tendon-driven finger. Shape memory alloy offer other interesting solution, using the shape transformation of the wire/structure in the moment of applying a thermal type transformation able to offer the martensitic temperature. An extension function is used in order to model the routing of each tendon. The kinematics of the tendon network, combined with the dynamics of the mechanism is applied to a two-link tendon-driven finger using shape memory actuation. Numerical simulations are presented and observations are formulated. Key-Words: - robotic finger, shape memory alloy, mathematical modeling, numerical simulation. 1 Shape memory alloy materials The shape memory effect was first noted over 50 years ago; it was not until 1962, however, with the discovery of a nickel titanium shape memory alloy but Buehler, that serious investigations were undertaken to understand the mechanism of the shape memory effect. The shape memory alloys possess the ability to undergo shape change at low temperature and retain this deformation until they are heated, at which point they return to their original shape. The nickel titanium alloys, used in the present research, generally refereed to as Nitinol, have compositions of approximately 50 atomic % Ni/ 50 atomic % Ti, with small additions of copper, iron, cobalt or chromium. The alloys are four times the cost of Cu-Zn-Al alloys, but it possesses several advantages as greater ductility, more recoverable motion, excellent corrosion resistance, stable transformation temperatures, high biocompatibility and the ability to be electrically heated for shape recovery. Shape memory actuators are considered to be low power actuators and such as compete with solenoids, bimetals and to some degree was motors. It is estimated that shape memory springs can provide over 100 times the work output of thermal bimetals. The use of shape memory alloy can sometimes simplify a mechanism or device, reducing the overall number of parts, increasing reliability and therefore reducing associated quality costs. Because of its high rezistivity of 80 – 89 micro ohm-cm, nickel titanium can be self heated by passing an electrical current through it. The basic rule for electrical actuation is that the temperature of complete transformation to martensite Mf, of the actuator, must be well above the maximum ambient temperature expected. The alloys and manufacturing techniques improved, so did the experience and results of experimenters. Nitinol received much attention for medical applications, toys industry, teleoperated systems and robotics, especially autonomous robots. In 1989 Oaktree Automation Inc, in Alexandria Virginia, started developing the Finger spelling Hand, an anthropomorphic robotic device to serve as a tactile communication aid for deaf - blind individuals, particularly those unable to read Braille. The device used a total of one hundred and eight 250 µm Flexinol wires acting in parallel. The most successful applications of shape memory alloy components usually have all or most of the following characteristics: Ü A mechanically simple design Ü The shape memory component pops in place and is held by other parts in the assembly Ü The shape memory alloy component is in direct contact with a heating/cooling medium Ü Friction is minimized and no complex stresses or stress concentrations are present Ü A minimum force and motion requirement for the shape memory component Ü The shape memory component is isolated from incidental forces with high variation Ü The tolerances of all the components realistically interface with the shape memory component. Based on description of shape memory alloy