Position control of a spherical joint using feedback linearization for SMA wire actuators

Shape memory alloys (SMAs) offer great potential as an actuation modality. They possess high power densities and are easily miniaturized. However, the use of SMAs has been limited by the fact that they are difficult to control. In this work, a model of SMA behavior is presented. An I/O linearizing controller is derived and a temperature observer is formulated using this model. The efficacy of this controller is then demonstrated for position control of a single degree of freedom (DOF) joint and a novel 3 DOF spherical joint that is suitable for small-scale robotic manipulators and wrists.