Nondimensional analysis and experimental assessment of the PII1/2DD1/2 position control of a rotary axis

Fractional Order controllers, based on derivatives and integrals of non-integer order, represent a propitious and promising research area since they can improve the performance of mechatronic systems compared to traditional Integer Order PID controllers without requiring hardware upgrades, but only using their higher tuning flexibility. Nevertheless, Fractional Order controllers are still rarely applied in real automation tasks, since their tuning is more complex and in general requires a model-based optimization for full exploitation of their capabilities. Recently, the PII^1/2DD^1/2 controller has been proposed, extending the classical PID by introducing a half-integral and a half-derivative term. A Bode plot-based tuning method has been presented for this controller, deriving the PII^1/2DD^1/2 parameters from a given set of PID gains. This method enables a significant reduction in tracking error for position control of a mechatronic axis without the need for complex model-based optimizations. In this paper, the previous results of this PII^1/2DD^1/2 tuning methodology have been generalized by employing a nondimensional approach. This approach highlights the conditions under which the benefits of this Fractional Order controller over the PID are most significant. The findings have been validated through experimental tests on a rotary axis, confirming the correctness and usefulness of the method.