SHAPE MEMORY ALLOY SERVO ACTUATORS

THE RECENT RESURGENCE OF RESEARCH ACTIVITIES ON SHAPE MEMORY ALLOYS (SMA) HAS ADVANCED THEIR APPLICATION INTO NEW AREAS. BY CONTROLLING THE ALLOYING MATERIALS AND INGREDIENTS, THE SHAPE TRANSFORMATION CAN BE MADE TO OCCUR AT PRECISE TEMPERATURES, THUS ENABLING SMAS TO FIND APPLICATIONS IN THERMOSTAT ACTUATORS AND COUPLINGS. BY TAKING ADVANTAGE OF SMA'S DYNAMIC PROPERTIES, ACTIVE CONTROL OF THERMAL HEATING AND COOLING PERMITS THE ALLOY'S USE IN ROBOTIC MANIPULATORS AND MECHANISMS. THE TI-NI ALLOY (NITINOL) WILL BE USED DUE TO ITS SUPERIOR STRESS/STRAIN CHARACTERISTICS, HIGH RESILIENCE, AND CORROSION RESISTANCE. THREE TYPES OF POSITIONING DEVICES ARE TO BE IMPLEMENTED AND ANALYZED TO OBTAIN ENGINEERING DATA ON THEIR PERFORMANCE CAPABILITIES; A TRANSLATIONAL ACTUATOR, A ROTATIONAL ACTUATOR, AND AN ACTIVE CATHETER. JOULE HEATING WILL BE USED AS THE CONTROL MECHANISM DUE TO TI-NI'S HIGH RESISTIVITY. A POSITION FEEDBACK CONTROL LOOP WILL BE ESTABLISHED BY MONITORING THE RESISTANCE OF TI-NI WIRE DURING ITS PHASE TRANSFORMATION. NEW CONTROL ELECTRONICS WILL BE DEVELOPED TO PROVIDE GENERAL PURPOSE CONTROL OF SMA SERVO ACTUATORS. POSITION AND FORCE CONTROL WILL BE DEMONSTRATED USING AN EXTERNAL POSITION ENCODER. ADDITIONAL STUDIES ARE PLANNED INCLUDING THE FEASIBILITY OF USING SEMICONDUCTOR THERMALELECTRIC COOLING OF SMA WIRE.