Fractional-order control of a micrometric linear axis

This paper discusses the application of a particular fractional-order control scheme,the pdd1/2,to the position control of a micrometric linear axis. the pdd1/2 scheme derives from the classical pd scheme with the introduction of the half-derivative term. the pd and pdd1/2 schemes are compared by adopting a nondimensional approach for the sake of generality. the linear model of the closed-loop system is discussed by analysing the pole location in the σ-plane. then,different combinations of the derivative and half-derivative terms,characterized by the same settling energy in the step response,are experimentally compared in the real mechatronic application,with nonnegligible friction effects and a position set point with trapezoidal speed law. the experimental results are coherent with the nonlinear model of the controlled system and confirm that the introduction of the half-derivative term is an interesting option for reducing the tracking error in the transient state. © 2013 luca bruzzone and pietro fanghella.