On the realization of an accurate hydraulic servo through an iterative learning control

Abstract

Many hydraulically-operated process such as machining, injection molding and metal forming process are usually represented by a hydraulic actuator-load system whose dynamic characteristics are complex and highly nonlinear. Due to these characteristics, the conventional approach to the controller design for these systems may not guarantee accurate tracking control performance. Taking into account the repetitive nature of the operations in those processes, a discrete iterative learning control algorithm is proposed to realize an accurate hydraulic servo system. In the algorithm, the control input sequence for next operation is determined by utilizing the tracking error as well as information of the dynamic characteristics obtained from the past operations such that the output trajectory tracks the given desired trajectory as closely as possible. To investigate gradual improvement of tracking performance in consecutive operations, the proposed algorithm is implemented to the hydraulic servo system. A series of experiments was performed for the position tracking control of the system. The experimental results show that regardless of inherent nonlinearities and uncertainties associated with hydraulic system, an accurate tracking control performance is obtained using the proposed learning control algorithm characterized by recursive operations.