Recently the Time Delay Control (TDC) method has been proposed as a promising technique in the robust control area, where the plant has unknown dynamics with parameter variations, and substantial disturbances are present. When TDC is applied to the plant with hard nonlinearity(saturation/friction), undesirable responses appear.
First, when TDC is applied to the plant with saturation nonlinearity, windup phenomena arise, leading to excessive overshoot and instability. As a remedy of this problem, anti-windup methods for TDC have been proposed. The stability of the overall system has been analyzed for a class of LTI MIMO system. The effectiveness for the proposed method has been shown with simulation and experimental results.
In the next, when TDC is applied to the plant with friction nonlinearity, in which static friction is dominant, stick-slip phenomena are observed to arise, causing limit cycle in steady-state. First of all, friction model have been investigated, which can represent friction phenomena, and then, by the simulation, it has been confirmed that stick-slip phenomena occur. In order to solve the problem, stick-slip compensator for TDC have been proposed. The effectiveness for the stick-slip compensator has been shown with simulation. For the experiment, the pneumatic cylinder system have selected, which is well-known that static friction is dominant among mechanical systems. Experimental results show that stick-slip problem has been observed without compensator and has been remedied with compensator.
Through this research, it was verified that TDC with compensators has a robust property where plant has hard nonlinearity(saturation/friction).
