Suppression of limit cycle and improvement of robust performance in two-mass resonant systems with nonlinearity

Two-mass systems are shown as a model of two masses connected by a spring and often seen in mechanical systems. PID control, resonance ratio control, H/sup /spl infin// control, and etc. have been applied to the two-mass systems. Conventional controllers that use a disturbance observer for two-inertia systems are adopted. A systematic parameter design method for the systems is proposed, where a load variation, Coulomb friction, and fast and precise control are considered. For limit cycle due to friction, a suppression condition of limit cycle is derived by an analysis using a describing function method. For load variation, robust stability for time varying system with structured uncertainty is guaranteed by the quadratic stability. Moreover, nominal performance is improved by maximizing the smallest eigen value of control system under the above restrictions. Effectiveness is confirmed by some simulations and experiments.