New Dead⁃zone Compensation Approach for Proportional Flow Valve

To solve the dead⁃zone in the output flow curve of the proportional flow valve without displacement sensor,a dead⁃zone compensation approach is proposed in this paper.Instead of detection and feedback of the valve spool position,the proposed approach adopted the pressure drop across the valve metering orifice to accomplish the dead⁃zone compensation.The first step was to test and get the_(max)imum output flow,Q_(max),at a preset reference pressure drop,such asΔP_(0).The next step was to construct the target compensation flow curve,which is a line through(0,0)and(ΔP_(0),Q_(max)).Then a compensation law was designed to approach the target curve.However,the research results show that the above strategy caused over⁃compensation once the actual pressure drop deviated fromΔP_(0).Thus a correction coefficient,β,was presented to correct the initial compensation law as the pressure drop deviated fromΔP_(0).For example,the test results indicate that the corrected compensation approach could reduce the dead⁃zone from 53.9%to 3.5%at a pressure drop of 1 MPa;as the pressure drop was increased to 5 MPa,the dead⁃zone was reduced from 51.7%to 3.5%.Therefore,the following conclusions can be drawn:the proposed compensation approach is feasible,which can effectively reduce the dead⁃zone and improve the output flow static performance of the proportional flow valve without spool displacement feedback.

Model-based trajectory tracking control for an electrohydraulic lifting system with valve compensation strategy

The natural frequency of the electrohydraulic system in mobile machinery is always very low,which brings difficulties to the controller design.To improve the tracking performance of the hydraulic system,mathematical modeling of the electrohydraulic lifting system and the rubber hose was accomplished according to an electrohydraulic lifting test rig built in the laboratory.Then,valve compensation strategy,including spool opening compensation (SOC) and dead zone compensation (DZC),was designed based on the flow-pressure characteristic of a closed-centered proportional valve.Comparative experiments on point-to-point trajectory tracking between a proportional controller with the proposed compensations and a traditional PI controller were conducted.Experiment results show that the maximal absolute values of the tracking error are reduced from 0.039 m to 0.019 m for the slow point-to-point motion trajectory and from 0.085 m to 0.054 m for the fast point-to-point motion trajectory with the proposed compensations.Moreover,tracking error of the proposed controller was analyzed and corresponding suggestions to reduce the tracking error were put forward.