Flow match and precision motion control of asymmetric electro-hydrostatic actuators with complex external force in four-quadrants

Asymmetric Electro-hydrostatic actuators (EHAs) have been widely applied in the aerospace and manufacturing industries owing to their small installation space. However, some challenges must be considered in precision control. First, a deficient or excess flow rate forms in the closed hydraulic circuit because of the different piston areas between the cap and rod sides of the asymmetric actuators. In addition, a complex external force, which is difficult to measure directly, always emerges and declines the control performance when EHAs are operated. In this study, a modified hydraulic circuit and an integrated flow-matching valve were developed to address the mismatched flow rate. Subsequently, a high-performance motion control scheme was proposed based on the extended state observer (ESO) and backstepping method. Within this controller, the forward dynamic compensation was designed in terms of the four-quadrant flow compensation model. Meanwhile, the nonlinear gain and updated law of compensations for observer error were synthesized to suppress tracking errors. Comparative experiments demonstrated the higher precision tracking performance of the proposed motion controller in all four quadrants.