The speed control problem of a time-delay DC motor system is proposed because the control performance can severely deteriorate under uncertain delay time information. Since most of existing delay compensators require exact system parameters and delay time information, the performance improvement has been limited under delay time uncertainty. The proposed method incorporates a disturbance observer on the slave side of the system with a communication disturbance observer that does not require the delay time information for generating a predicted output signal. The effectiveness of the proposed algorithm is tested through comparative simulations and experiments using a testbed system under large delay time uncertainty.

A robust speed controller for a time-delay DC motor system is presented under large delay time uncertainty. Unlike a recent result relying on a disturbance observer on the slave side of the system, a new delay compensator is devised and combined with a lowpass filter to improve its robustness against uncertain delay times and external disturbances. The effectiveness of the proposed method is tested through comparative simulations and experiments using a testbed system.

-This paper presents a robust position controller for a one degree-of-freedom (DOF) mechanical system using only position measurement. In order to alleviate the performance degradation owing to various uncertainties, a two-stage design method is studied by employing a proportional integral observer (PIO). In the first stage, a baseline backstepping controller is designed for a nominal system without accounting for uncertainties. The PIO is developed for estimating both the velocity information for the backstepping controller and an equivalent input disturbance for a feedforward compensation using the estimated uncertainty. It is shown that the estimation errors with the proposed PIO can be made arbitrarily small in a finite time. If the system suffers from undesirable actuator nonlinearities, however, it might be necessary to estimate the velocity and the disturbance with different rates of convergence. The proposed method combines the predesigned backstepping controller and dual PIOs to reduce mechanical vibrations as well as steady-state errors. The performance of the proposed method is tested through comparative computer simulations and experiments using a laboratory prototype.