Effect of Actuator Torque Degradation on Behavior of a 6-DOF Industrial Robot

Le Ngoc Truc,Nguyen Trung Thanh,Tung Lam Nguyen,Nguyen Tuan Nghia,Nguyen Minh Thien

doi:10.13189/ujme.2020.080206

Abstract

Actuator faults of robot manipulators may occur during their lifetime after long time in operation. There are several kinds of actuator failures such as locked joints, free-swinging joints, and loss of actuator torque effectiveness. The main goals of this paper are (i) to classify the loss of torque effectiveness, called torque degradation, into three divergent cases: Boundary Degradation of Torque (BDT), Boundary Degradation of Torque Rate (BDTR), and Proportional Degradation of Torque (PDT); and (ii) to analyze their effect on behavior of a typical industrial robot. The possible failures might degrade the whole system performance or in some certain cases leading to unavoidable damages. In normal operation, we do not have a controller designed specifically for these faults. In order to have a better understanding on how the mentioned problems affect robot operations, with an assumption that the knowledge of robot parameters are known, a closed-loop control law is used to demonstrate the control ability in dealing with these cases. By taking advantage of MATLAB/Simscape Multibody, the quasi-physical model of robot is employed instead of expensive prototypes and experiments. Simulation results show that the joint responses according to different types of failures. In many cases, the robot cannot track the reference trajectories properly.

Highlights

For many years, researches in the field of robot man ipulators have received a large amount of attention, especially in card inal industries because of the ability to replace people working in hazardous and risky environments with h igher flexib ility and precision [1]–[4]
In [5], the locked joint failure was addressed with matrix perturbation methodology which is extended to deal with mu ltiple locked joint failures
Robotic arms may be subject to effect of actuator torque degradation faults

Summary

Introduction

Researches in the field of robot man ipulators have received a large amount of attention, especially in card inal industries because of the ability to replace people working in hazardous and risky environments with h igher flexib ility and precision [1]–[4]. In [7], the problem of how to optimally readjust a kinemat ically redundant manipulator in anticipating a free-swinging failure was presented These studies for actuator failures just mentioned locked jo int faults or free-swinging joint faults. Robotic arms may be subject to effect of actuator torque degradation faults. This actual problem should be considered to suggest approaches to compensate for failures and improve man ipulator effectiveness. In [16], a model-based fault detection and isolation method for robotic arms based on adaptive nonlinear observer was proposed to deal with two cases: actuator and sensor faults. A study on the effect of actuator torque degradation faults of a six degree of freedom (6-DOF) manipulator has considerable differences

Objectives

Results

Conclusion