A Control Strategy for Electro-hydrostatic Actuator Considering Static Friction, Resonance, and Oil Leakage

Abstract

Electro-hydrostatic actuators (EHAs) are hydraulic systems that operate without control valves, making them a compact, cheap, and highly energy efficient system. However, resonance, static friction, and oil leakage degrade their control performance. Three controllers are integrated to overcome these issues. First, static friction is suppressed by a feedback modulator (FM). Input torque is quantized to exceed the maximum static friction force, and quantization errors are suppressed by the FM. Second, resonance is canceled out by a self resonance cancellation (SRC) technique. In the SRC, both angle responses of a hydraulic pump and a hydraulic motor are measured, and the rigid body mode is extracted. Then, resonance becomes unobservable, changing the system as a second-order system. Third, modeling errors, including oil leakage, are suppressed by a self resonance cancellation disturbance observer (SRCDOB). As the SRCDOB is implemented in the rigid body mode, the cutoff frequency of the SRCDOB can be greater than that of most common disturbance observers. This combination of controllers drastically improves the control performance, and it enables control system design based on frequency.

Delay Analysis and the Control of Electro-Hydrostatic Actuators

“…Reference [27] used quantitative feedback theory to optimize the steady-state and transient position tracking performances, but the EHA they used in their study did not show a delay. In [28], a combination with a feedback modulator, self-resonance cancellation, and a self-resonance cancellation disturbance observer was used and it drastically improved the control performance. They conducted the methods on a traditional EHA system, so they did not use the hydraulic lock and the delay was not obvious in their study.…”