Robust Motion Control of DC Servo Systems With Saturation Nonlinearity and Control Effort Constraint

In this work, the robust motion control issues of a dc servo system with parametric uncertainty, disturbances, control effort constraints, and saturation nonlinearity are addressed using the quantitative feedback theory (QFT). Fast tracking of large set-point changes without activating the saturation nonlinearity constraint poses a significant challenge in control design that is highly critical for modern industrial servo applications, wherein minimal control effort is desired. To achieve this, a new QFT design is proposed, which not only guarantees the robustness, but also ensures closed loop stability preventing saturation nonlinearity using the Popov criterion. The inclusion of control effort constraint guarantees the control input to be within the limits. In addition to achieving fast tracking of large set-point changes and disturbance rejection, the proposed QFT design also allows the handling of the saturation nonlinearity with smaller control input and simpler controller structure, which does not require any tuning. To demonstrate the effectiveness of the proposed QFT design, experiments are conducted on a practical dc servo system, which validate the fast and accurate tracking performance of the proposed scheme with a smaller control input.