Active Fault Tolerant Control System Design for Hydraulic Manipulator With Internal Leakage Faults Based on Disturbance Observer and Online Adaptive Identification

Hoang Vu Dao,Kyoung Kwan Ahn,Duc Thien Tran

doi:10.1109/access.2021.3053596

Abstract

In this paper, an active fault-tolerant control (FTC) system design is proposed for an n-degree-of-freedom (n-DOF) hydraulic manipulator with internal leakage faults and mismatched/matched lumped disturbances. A pair of matched and mismatched disturbance observers (DOBs) is proposed to simultaneously estimate and compensate for the effects of matched/mismatched disturbances on the control system in healthy conditions. The fault detection is achieved when the estimated matched disturbance is larger than a threshold. After that, a novel control reconfiguration law is designed to switch from a normal controller to a fault-tolerant controller with an online identification algorithm based on an adaptive mechanism. The proposed active FTC guarantees the position tracking performance in not only single-fault but also simultaneous-faults conditions. Moreover, the problem of uniting disturbance-observer-based control for external disturbance and adaptive control for parametric uncertainty is solved in a novel approach. Simulation results are conducted in a two-degree-of-freedom hydraulic leg prototype, which verifies the effectiveness of the proposed method.

Highlights

Electrohydraulic servomechanism has a high-power-to-weight ratio and large force/torque output compared to servo systems driven by pneumatic or electrical actuators [1]
This paper proposes an active fault-tolerant control (FTC) system design for a hydraulic manipulator with internal leakage faults and matched/mismatched disturbances
A novel fault detection law is proposed to detect the internal leakage fault that occurs in each joint based on the estimated matched disturbances from the matched disturbance observers (DOBs)

Summary

INTRODUCTION

Electrohydraulic servomechanism has a high-power-to-weight ratio and large force/torque output compared to servo systems driven by pneumatic or electrical actuators [1]. The performance of the servo system driven by electrohydraulic actuators usually is strongly affected by highly nonlinearities, modeling uncertainties (e.g., Bulk modulus, friction, and leakage), and external disturbance (e.g., load variations) [12], [13] To deal with these problems, several approaches have been proposed. After the fault is detected, the controller is reconfigured, i.e., the ESO which is utilized to estimate the matched disturbance is turned off, and the online identification algorithm based on adaptive law is turned on to effectively estimate the internal leakage fault coefficient which is the dominant component compared to the matched disturbance due to the severity of its effects on the system performance Based on this approach, merging the DOB and adaptive mechanism is achieved in this work to effectively take advantage of both techniques. Where d τd (q)Fa represents lumped disturbance and uncertainty vector

HYDRAULIC SYSTEM

DISTURBANCE OBSERVER DESIGN

ONLINE-FAULT IDENTIFICATION

STABILITY ANALYSIS

NUMERICAL SIMULATION

CONCLUSION