New strategy of nonlinear PD controller for hydraulic force system under large variation of load stiffness

A nonlinear PD controller is developed in new strategy to keep acceptable performance of an electro-hydraulic force system in the condition of large variation of stiffness and load. The controller uses two nonlinear tracking differentiators to obtain high quality differential signals. New approach is adopted to build the nonlinear gain functions and experiential formulas are given to determine the range of the gains. Simulation contrast shown that the performance of new functions is better than original. The experimental results indicate that high performance can be guaranteed and the control algorithm is simple to realize in engineering.