Application of Advanced Control Theory to Fluid Power Control

This paper presents high performance control of electrohydraulic actuators for generating near periodic time varying trajectories. Such type of trajectories can be found in many industrial applications, particularly those involving master-slave type electronic cam-follower motion generation. The control algorithm includes a robust feedback control for disturbance rejection, a repetitive control to compensator for periodic signals, and a previewed feedforward control for tracking time varying signals. The three control actions are numerically solved simultaneously by formulating the control problem as a μ-synthesis problem. The μ-synthesis formulation includes practical design constraints by imposing frequency domain bounds of disturbance rejection, model matching error for tracking, unmodeled dynamics for robust stability, a periodic signal generator in the repetitive control, and a delay filter that corresponds to the preview length of the feedforward compensator. The proposed control design approach is applied to an electrohydraulic actuator to generate cam lobe profiles for cam shaft machining application. Control realization issues including model structure of electrohydraulic actuators, characterization of system model and uncertainty bounds, and controller order reduction for real-time implementation by digital signal processors are discussed. Experimental results are presented to demonstrate the design process and control performance.