As a hydraulic actuator is used over time, the piston seal that closes the gap between the moveable piston and the cylinder wall wears. This results in the fluid to eventually being able to flow across the piston and between the cylinder chambers. Although no fluid is lost from the circuit, the dynamic performance of the system is affected since only a portion of the flow delivered to the actuator is available to move the piston against the load. Leakage across the piston introduces a flow deadband, which can lead to servoing errors. This paper presents an approach based on the cross-correlation time-series analysis to determine the health of hydraulic actuator internal seals. Pressure signals obtained directly from routine operations are analyzed using the cross-correlation function. The method presented in this paper is shown to be capable of detecting leakages as small as 0.069 l/min.

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