Robust Tracking for Uncertain Flexible Structures Using Mixed Time-Optimal and Sliding Mode Control

An improvement step in robust control is studied for uncertain (linear or nonlinear) systems. The proposed two-stage control scheme first modifies the original desired trajectory, and then imposes robustness against uncertainties in tracking this modified trajectory. For the trajectory modification stage, a simple scheme is considered : time optimal-rigid body motion (TO). The robustness stage is performed using Sliding Mode Control with Perturbation Estimation (SMCPE), an advanced form of SMC. This routine brings some strong features as demonstrated by examples. A rotating hub with flexible beam attachment is taken as the first example, and an undercontrolled two-mass system with a linear spring as the second. The comparative studies show superior results for the combination of TO-SMCPE over the basic SMCPE. Moreover, this two-stage control exhibits stable and highly advantages performance even for cases where H∞-type of robust control structure is declared unstable by earlier investigations.