The paper presents a study on speed control of hydraulic linear actuators without servo valves. A typical hydraulic circuit including a cylinder, a set of four throttle valves and four high frequency directional control valves is executed. Characteristics of components are mathematically modeled and numerically investigated in MATLAB/Simulink. The research exploited combination of rule-based control algorithm and pulse-width modulation for oil flow rate control, hence leading to control of piston speed. The control process is carried out in two stages. At the first stage, the rule-based control algorithm makes piston speed track the set value with rough error. Pulse-width modulation is applied on a certain high frequency valve will help speed almost match the desire one at the second stage. The obtained simulation results show that speed tracking control is guaranteed. Thus, the advantages of pulse-width modulation control are not only promoted, but the pulse regulation frequency for high-speed on/off valve is also significantly reduced. The control method can be considered as an effective solution for accurately controlling the speed of the hydraulic systems instead of using servo valves.
