A robust observer and controller design for a DC motor with a low-resolution encoder

This work focuses on the problem of high-performance robust control of a dc motor in the presence of a low-resolution position encoder. An observer assisted feedback control scheme is presented in which a robust extended high-gain observer (EHGO) is designed for simultaneous estimation of motor speed and lumped system uncertainties. The conventional approach of calculating speed by direct differentiation of encoder pulses is superseded by the EHGO technique that allows significant reduction in quantization noise associated with the encoder without requiring a low-pass filter. For the speed control problem, an improved integral sliding mode controller is proposed with a sigmoid boundary layer. The integral action compensates for the boundary layer error thereby guaranteeing tracking error convergence to zero. Stability, robustness and accuracy of the proposed observer and controller are established mathematically. Simulations and experimental tests are carried out that validate the given scheme.