Modeling and control of SMA helical spring actuated unconventional locomotion systems

Miniature and bio mimicking robots cannot be equipped with conventional electromechanical actuators due to larger size and weight. Shape Memory Alloys (SMA) are a potential choice in such systems. Large deflection systems are designed using SMA helical springs. Temperature induced phase transformation causes the strain in such systems. In bio mimicking and bio inspired designs, SMA´s are often considered as an equivalent to an artificial muscle. Such systems require sub millimeter diameter SMA helical spring actuators working independently or in recruitment. The small physical size of actuator arises practical issues in measuring the temperature over sub millimeter helical springs. This paper introduces a sensorless temperature estimation method for SMA helical actuators and introduces simple mechanism using SMA sub millimeter helical actuator.