A dual EHA system for the improvement of position control performance via active load compensation

The dynamic response of a single-rod type EHA (electro-hydrostatic actuator) in the closed-loop control of piston position is inherently dependent on load directions due to the unequal piston areas of the rod-side and head-side. In particular, the response time of the extension and retraction of the piston rod changes significantly when the direction of the external load is changed. In this study, a dual EHA system is proposed, where a force-controlled double-rod type EHA was added to a single-rod type EHA to isolate it from external loads. Force signals for the force control were obtained by measuring the cylinder chamber pressures. The dual EHA system exhibited significantly improved position control performance, even when using basic proportional controllers. An expected collateral benefit is that the system may be reconfigured to a redundant system for fail-safe operation in the emergency case where the main position controlled EHA is malfunctioning.