In recent years, sliding mode control has been suggested as an approach for the control of systems with nonlinearities, uncertain dynamics and bounded input disturbances. The most distinguished feature of the sliding mode control technique is its ability to provide fast error convergence and strong robustness for control systems in the sense that the closed loop systems are completely insensitive to nonlinearities, uncertain dynamics, uncertain system parameters and bounded input disturbances in the sliding mode. Figure 1 shows an example trajectory of a system under sliding mode ontrol. The sliding surface is described by s = 0, and the sliding mode along the surface commences after the finite time when system trajectories have reached the