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A dead-band model and its online detection for the pilot stage of a two-stage directional flow control valve

The dead-band in the electro-hydraulic proportional control valve is one of the main factors that affect its dynamic performance. Especially in the pilot stages of two-stage directional flow control valves, the insistent dead-band will result in a conservative valve controller design. In this paper, a detailed dead-band model describing the relationship between pilot valve spool and the flow rate of the pilot control valve is proposed. And an improved dead-band description involved with the housing clearance of the valve spool is developed to prove the dead-band uncertainty for a single valve system. Then a simple and effective method is proposed to detect the varying dead-band values in the pilot stage. This method is specially designed with a limited main spool displacement and short time interval so that it can be used for online detection without affecting the hydraulic system where the two-stage valve is involved. With the regular dead-band inverse function, comparative experimental results show that this method is effective to attenuate the large trajectory tracking error caused by the varying dead-band. This dead-band detection also can be applied to other electro-hydraulic proportional valve-controlled position control systems with unknown dead-bands.