Detection and Isolation of Leakage and Valve Faults in Hydraulic Systems in Varying Loading Conditions, Part 1: Global Sensitivity Analysis

Abstract

Model-based condition monitoring methods are widely used in condition monitoring. They usually rely on ad hoc approaches to verify the system model and then best practices are reported to detect the given set of faults. This first part of a two-piece paper introduces a generic Global Sensitivity Analysis-based approach that can be applied systematically to verify the model parameter sensitivities used for the model-based fault detection. The case study is a generic servo valve-controlled hydraulic cylinder with unknown loading condition which is then systematically analyzed with Global Sensitivity Analysis. The method shows valuable insight into systematic model verification and resulting fault detection in terms of showing the dominant sensitivity of the nominal flow rate and nominal pressure difference, and the exact sensitivities of 0 -1 dm 3 /min external and internal leakages on cylinder chamber pressures and velocity. In the second paper, an Unscented Kalman Filter-based Fault Detection and Isolation scheme for leakage and valve faults of a generic servo valve-controlled hydraulic cylinder is devised and fault patterns are presented.

Detection and Isolation of Leakage and Valve Faults in Hydraulic Systems in Varying Loading Conditions, Part 2: Fault Detection and Isolation Scheme

“…It has a 4/3-directional valve that controls the joint cylinder, and three restrictor valves which emulate external leakages between the cylinder and the directional valve ('External leakage A' and 'External leakage B') and internal leakage across cylinder chambers ('Internal leakage'), for a list of system components see (Nurmi and Mattila 2011). In (Nurmi and Mattila, 2011), the model and GSA of the test bed were presented. In this paper, we use that model to simulate valve faults and utilize the GSA results in the verification of the UKF process model and in the development of the fault detection scheme.…”

“…The flow coefficients, shown to be sensitive parameters and treated as constants in the GSA (Nurmi and Mattila, 2011), were not constants but nonlinear functions of spool position. To improve modelling accuracy each flow coefficient was fitted to a thirdorder polynomial (Muenchhof and Beck, 2008):…”

“…Consequently, the discrete-time state space representation from (Nurmi and Mattila, 2011), Eq. 22, reduces to: In the GSA in (Nurmi and Mattila, 2011), the effective bulk moduli B effA and B effB were shown to be somewhat influential in transients, so effort was used to correctly identify them.…”

“…22, reduces to: In the GSA in (Nurmi and Mattila, 2011), the effective bulk moduli B effA and B effB were shown to be somewhat influential in transients, so effort was used to correctly identify them. They were found to be dependent on piston position.…”

“…Therefore, this scheme is more viable in generic hydraulic systems where the load can vary during operation. This paper utilizes the model and Global Sensitivity Analysis (GSA) that was presented for our test bed in (Nurmi and Mattila, 2011). This combines into a systematic approach to modelbased condition monitoring compared to the ad hoc approaches currently present.…”