A Novel Active Fault-Tolerant Tracking Control for Robot Manipulators with Finite-Time Stability.

Thanh Nguyen Truong,Anh Tuan Vo,Hee-Jun Kang,Mien Van

doi:10.3390/s21238101

Abstract

Many terminal sliding mode controllers (TSMCs) have been suggested to obtain exact tracking control of robotic manipulators in finite time. The ordinary method is based on TSMCs that secure trajectory tracking under the assumptions such as the known robot dynamic model and the determined upper boundary of uncertain components. Despite tracking errors that tend to zero in finite time, the weakness of TSMCs is chattering, slow convergence speed, and the need for the exact robot dynamic model. Few studies are handling the weakness of TSMCs by using the combination between TSMCs and finite-time observers. In this paper, we present a novel finite-time fault tolerance control (FTC) method for robotic manipulators. A finite-time fault detection observer (FTFDO) is proposed to estimate all uncertainties, external disturbances, and faults accurately and on time. From the estimated information of FTFDO, a novel finite-time FTC method is developed based on a new finite-time terminal sliding surface and a new finite-time reaching control law. Thanks to this approach, the proposed FTC method provides a fast convergence speed for both observation error and control error in finite time. The operation of the robot system is guaranteed with expected performance even in case of faults, including high tracking accuracy, small chattering behavior in control input signals, and fast transient response with the variation of disturbances, uncertainties, or faults. The stability and finite-time convergence of the proposed control system are verified that they are strictly guaranteed by Lyapunov theory and finite-time control theory. The simulation performance for a FARA robotic manipulator proves the proposed control theory’s correctness and effectiveness.

Highlights

Robot manipulators are widely used in the industrial manufacturing and service industries due to their persistence in operation, repetitive works, flexibility, heavy jobs, as well as requirements of high accuracy
By utilizing the proposed fault diagnosis observer (FDO)’s accurate fault information, the control system performance was significantly improved when the faults occur in the robot system
From the results presented in the two cases above, we can conclude that the proposed control strategy provided outstanding performance in terms of tracking error accuracy, fast convergence speed, smooth control torque, and strong fault-tolerant ability compared to the three remaining controllers

Summary

Introduction

Robot manipulators are widely used in the industrial manufacturing and service industries due to their persistence in operation, repetitive works, flexibility, heavy jobs, as well as requirements of high accuracy. Safety and high tracking performance are expected for many tasks that are a challenge in robot operation. The main challenges that interfere with the safety and operation of the robot can be included complex system dynamics, nonlinearities, frictions, external disturbances, uncertainties, faults, etc. They can provide the expected performance and safety under the influence of uncertainties when no faults occur in the system. Safety is seriously affected and control performance is reduced, leading to system instability. These affect the quality of the product, increasing the danger in the work environment with the presence of people. Fault diagnosis (FD) and fault-tolerant control (FTC) have attracted a lot of attention for detecting faults and maintaining the expected performance of Markovian jump systems [1], nonlinear systems [2], or robot manipulators in the existence of multiple faults

Methods

Results

Conclusion