Interval Type-2 Fuzzy and Interval Type-2 Fuzzy Sliding-Mode Control for Angular Regulation of a VTOL Plant: An Experimental Study

This work presents the design and experimental validation of two interval type-2 fuzzy controllers for the angular regulation of a one-degree-of-freedom QNET VTOL plant: a fuzzy controller with a PD+I structure (IT2FL) and a hybrid fuzzy sliding-mode controller (IT2FL-SMC). Both run in a cascade scheme, with the outer loop handling angular position and an inner loop handling motor current. In the IT2FL-SMC, the discontinuous switching term of a conventional sliding-mode controller is replaced by an interval type-2 fuzzy reaching action, while the continuous term is derived from a second-order model of the plant identified experimentally. The footprint of uncertainty is tuned on the platform, and both controllers are compared against PID, conventional SMC, type-1 fuzzy, and type-1 fuzzy sliding-mode controllers under the same conditions. The tests include step-reference changes and physical eccentric-load disturbances applied in both directions. In reference tracking, the IT2FL gives the smoothest actuation, with the lowest total variation of the control input and the shortest settling time. Under both disturbances, the IT2FL-SMC gives the lowest integral absolute and squared errors, though with a more active control signal. The two controllers turn out to be complementary: one favors smooth actuation, the other favors disturbance rejection.