  This paper presents a new prescribed performance control scheme for the
attitude tracking of the three degree-of-freedom (3-DOF) helicopter system with
lumped disturbances under mechanical constraints. First, a novel prescribed
performance function is defined to guarantee that the tracking error
performance has a small overshoot in the transient process and converges to an
arbitrary small region within a predetermined time in the steady-state process
without knowing the initial tracking error in advance. Then, based on the novel
prescribed performance function, an error transformation combined with the
smooth finite-time control method we proposed before is employed to drive the
elevation and pitch angles to track given desired trajectories with guaranteed
tracking performance. The theoretical analysis of finite-time Lyapunov
stability indicates that the closed-loop system is fast finite-time uniformly
ultimately boundedness. Finally, comparative experiment results illustrate the
effectiveness and superiority of the proposed control scheme.
