Energy-efficient position control of an actuator in a digital hydraulic system using on/off valve

Hydraulic systems are widely used in different industries; especially where high-magnitude forces are exerted. Traditional elector-hydraulic systems use a proportional or servo valve to control the position of hydraulic actuators. Low energy efficiency and high cost of these control valves are two important problems in these systems. Digital Hydraulics is one of the most novel methods, proposed to address these issues. Low cost, better energy efficiency, contamination insensitivity and low leakage are major advantages of Digital Hydraulics which make them popular among researchers. In this paper a Digital Hydraulic circuit is proposed, that uses a fast-switching on/off valve instead of servo valves to control the position of a hydraulic actuator. For this purpose the flow running through the fast-switching valve is controlled, employing proper PWM duty cycle. The excess flow of pump is discharged to the tank directly instead of going through the relief valve when the control valve is off. Thus the wasted energy, caused by the relief valve, is reduced significantly. A robust H∞ controller is applied to guarantee position tracking in the presence of uncertainties. The effectiveness of this method is tested after conducting experiments on a hydraulic test rig and presenting the experimental results.