SINGLE LINK ROBOT ACTUATED WITH SHAPE MEMORY ALLOY Nicu-George Bîzdoacă, Daniela Pană, Sonia Degeratu, Elvira Bîzdoacă, Cristina Pană, Marius Niculescu University of Craiova, Faculty of Control, Computers and Electronics, 5 Tehnicii, 1100 Craiova E-mail: nicu@robotics.ucv.ro Abstract: The present paper explore the robotics control actuation using shape memory alloy tendon. Shape memory alloy offer an 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. This thermal transformation can be inducted using electrical current and a suitable control strategy. In order to assure an efficient control of SMA actuator applied to inverted pendulum, a mathematical model and numerical simulation of the resulting model is required. Due a particular possibility SMA actuator connection, a modified dynamics for wire or tendon actuation is presented. The control possibilities are explored: PI, PD and PID controller are connected to the single link SMA actuation. Numerical simulations are presented and observations are formulated. Key words: Robotics, numerical simulation, shape memory alloy actuation, mathematical model. 1. SHAPE MEMORY ALLOY 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, the experience and results of experimenters open the gates to the commercial applications. 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. Based on description of shape memory alloy materials, a SMA Simulink block was developed. The characteristic of material is idealized, but the approximations made are suitable for an efficient simulation. The user can indicate the start and stop martensitic and austenitic temperature and the force, momentum evolution. Fig. 1. Configurable model for shape memory alloy wire actuator