Reduction of hysteresis : a phase control approach

In this thesis, a controller design methodology to reduce hysteresis is introduced. Rate independent hysteresis is seen as an input-output phase lag, where the output can be saturated or not. The compensation is based on controllers derived from the Phaser, a frequency domain operator that shifts its periodic input signal by a phase angle &phis;, with unitary gain. When the phase angle varies, a variable phaser is shown to be able to handle minor hysteresis loops. The reduction of saturated or asymmetric hysteresis can be obtained using also the variable phaser. Practical implementations of these controllers are given and discussed. Two measures of performance are introduced to quantify the reduction of hysteresis and to compare the performance of different controllers.The controllers are implemented in simulations as well as in real systems to exemplify the use of these techniques, specifically in piezoceramic and shape memory alloy actuators. Given the experimental evidence that the feedback systems are stable, the stability of the feedback connection of systems represented by the Preisach model of rate independent hysteresis, and the phaser is shown theoretically