361 MINIMUM TIME ENERGY CONTROL FOR THE OPERATION TEMPERA'I'URE OF A NOVEL ELECTRa-MECHANICAL ACTUATOR A. Yeltekin, K. AI-Rubayi, E. Ayyappa Ohio ECE Dept., Athens Ohio 45701 Kevwords: electro-mechanical actuator, time problem, optimal control, dynamical model, heat transfer model Abstract In this work we will present modelling and optil'Tlal control of a prototype electro-mechanical actuator. The actuator consists of a shape memory al10Y which contracts when electrically charged and returns to its original length repetitively. To reduce the power consumption of the device we obtained a dynamical model for the distribution and found the optimal electrical energy which minimizes the weighted cost of energy and t inie. simulation results indicated that the minimum energy is 1.2% of the energy spend on previous experiments. INTRODUCTION In this work we will present the modellinq and optimal contra t of an experimental electra-mechanical actuator. The actuator is designed to be used in orthopedic appljance systems, especially in lower limb applications. The electro-mechanical actuator is l ight and consists of shape memory alloy (a heat st.abilized form of nitinol) wires which contract when heated by the electrical current passing through them. The prototype actuator is capable of generating 69.37 dyne (150 pounds) of pulling force during the contractions when activated using 947.6 joules of eleccrical energy. 'r',olO of the crucial design criteria are on the time response and energy consumption of the actuator. In order to use the actuator for functional 10',;er limb applications its time response should be compatible with the time-sequence of the human gait. The device has to be carried by the orthopedic pat.ients, hence its consumption should be low, so it can be activated with a battery. The actuator we will present here is our second prototype. First prototype and its model is presented in [Yeltekin]. In order to reduce the energy consumption of the device we obtained a dynamical model for the temperature distribution of the actuator and found the optimal electrical energy which minimizes the weighted cost of quadratic energy and time. simulation of the optimal input indicated that using the optimal activation, it is possible to reduce the total energy consumption to the 1.2% of the experimental energy consumption. Next section will explain the physical properties and the dynamical model for the actuator. DYNP..MICAL MODEL FOR THE ACTUATOR The actuator is working on the principle of contracting 4% of its length when heated by electricity. The actuator consists of 128 wires stretched in parallel in between two sets of end plates. The