An approach to reduction of hysteresis in smart materials

This paper addresses the problem of reducing the hysteresis found in the actuation of most smart materials. They are divided in two groups: systems with no saturation (e.g. piezoelectric actuators), and systems with saturation (e.g. shape memory actuators). For the control of the first group the concept of phaser is introduced, an operator which shifts the phase of a periodic signal but keeps its magnitude unchanged. Since it is possible to approximate phasers with linear filters, it is possible to design practical compensators. The design of a phaser requires the knowledge of one parameter φ, easily identified from experimental transfer function estimates. For the second group, two phasers are used in a tandem connection. One phaser is designed as described before, and the second is designed so as to vary with the input. This compensation reduces the hysteresis to a single saturation. To show its effectiveness, simulation results are provided using the hystery model, then the method is applied to an SMA actuator