SMA sensorless actuators for micrometric control

The ability of SMAs to respond reversibly to an external stimulus by modifying their dimensions can be used to generate motion or force in electromechanical devices and micro-machines. There are several works that demonstrate SMAs are serious alternatives as micrometric actuators, obtaining accuracies around 3 μm in position control if high-quality position sensors, such as LVDTs, are used to feedback position readings in the control loop. In this work, a SMA based actuator prototype has been developed, and so that it could be used in light-weight applications, the LVDT sensor used in previous works had to be replaced with a lighter alternative. Once several possible alternatives were analyzed, the possibility of using the wire's resistance as position sensor was chosen, that is, a sensorless control strategy was implemented. The experimental results show that it is possible to obtain accuracies around 60 μm, with the great advantage that the actuator could be reduced to a single SMA element without an additional sensor, question of great importance if the main goal is to reduce the overall weight, size and cost of the actuator.