H∞ position control of hard nonlinear systems

A nonlinear control scheme for preventing limit cycle due to the nonlinearity of the multistep bang-bang actuator in a mechanical position control system is proposed. A linearized model, sinusoidal input describing function (SIDF), for a multistep bang-bang actuator is introduced to compensate the nonlinearities. Using the model, an H_∞ robust controller is proposed using loop shaping techniques with normalized coprime factorization stabilization to address the robustness. The proposed controller needs a smaller deadband as a result of compensating the nonlinearity of the actuator. A single-axis servo system model is used to verify the proposed control scheme experimentally. Experimental results show that the controller is effective in suppressing undesirable persistent switching, and the performance was robust to changes in the controller gain