Laboratory experiments on fractional order PI control of a servo system with delay*

Fractional order controllers may guarantee an enhanced robustness of the controlled loops with respect to parameter variations of the plant. Moreover, their tuning rules offer more design degrees of freedom by taking advantage of the fractional order of differentiation and integration. In this paper, we experiment a loop-shaping method to tune fractional order PI controllers for servosystems reasonably described by a gain, an integrator, a time constant and a time delay. The aim is to verify the real applicability of the method by showing its simplicity and effectiveness in a concrete case, also in comparison with well-known rules used for tuning integer order PI. The tuning formulae are simple enough and the method guarantees satisfaction of performance specifications.