Practically Finite-Time ADRC for a 3-DOF Parallel Mechanism of PMAs With Couplings

In this paper, a practically finite-time active disturbance rejection control (PFTADRC) method is proposed for angle tracking on a 3-degree-of-freedom (3-DOF) parallel mechanism of pneumatic muscle actuators (PMAs) with couplings and disturbances. A coupling characterization is presented to determine whether the couplings are beneficial for the system. Based on this, a practically finite-time controller is designed, where detrimental and beneficial couplings are eliminated and remained, respectively. Moreover, when couplings change, the practically finite-time stability of the system is analyzed and guaranteed. Two Lyapunov criteria of practically finite-time stability are proposed to improve convergence rate of the system. Both the bounded region and the settling time are calculated. Finally, the numerical simulation results and experiment results are presented to illustrate the effectiveness of the proposed method.