Current Only-Based Fault Diagnosis Method for Industrial Robot Control Cables.

Heonkook Kim,Hojin Lee,Sang Woo Kim

doi:10.3390/s22051917

Abstract

With the growth of factory automation, deep learning-based methods have become popular diagnostic tools because they can extract features automatically and diagnose faults under various fault conditions. Among these methods, a novelty detection approach is useful if the fault dataset is imbalanced and impossible reproduce perfectly in a laboratory. This study proposes a novelty detection-based soft fault-diagnosis method for control cables using only currents flowing through the cables. The proposed algorithm uses three-phase currents to calculate the sum and ratios of currents, which are used as inputs to the diagnosis network to detect novelties caused by soft faults. Autoencoder architecture is adopted to detect novelties and calculate anomaly scores for the inputs. Applying a moving average filter to anomaly scores, a threshold is defined, by which soft faults can be properly diagnosed under environmental disturbances. The proposed method is evaluated in 11 fault scenarios. The datasets for each scenario are collected when an industrial robot is working. To induce soft fault conditions, the conductor and its insulator in the cable are damaged gradually according to the scenarios. Experiments demonstrate that the proposed method accurately diagnoses soft faults under various operating conditions and degrees of fault severity.

Highlights

Control and instrumentation (C&I) cables are utilized in a wide range of industrial applications, including nuclear power plants [1], ship power systems [2], vehicles [3], and factory automation [4], owing to their vital role in the control of motors and instrumentation of sensors
The most severe damage class is 28-cut class, which means in this class that 93.3 % of the conductor is damaged; the damaged wire is still working without indicating any fault symptom
Scenario 8 is to test for relatively slight damage classes, that is, 4 cut–12 cut, in which more than a half of the cross-sectional area of the conductor is intact, whereas, scenario 9 is to test for heavily damaged classes, that is, 16 cut–28 cut, in which less than a half of the cross-sectional area of the conductor is intact

Summary

Introduction

Control and instrumentation (C&I) cables are utilized in a wide range of industrial applications, including nuclear power plants [1], ship power systems [2], vehicles [3], and factory automation [4], owing to their vital role in the control of motors and instrumentation of sensors. And accurate diagnosis of faults reduces unwanted system downtime and improves the system reliability, resulting in the maximization of productivity. In modern automated manufacturing processes, a single fault in an industrial machine could cause an entire production line stoppage because the safety signals of machines are shared and controlled by a process control unit. Researchers have studied the faults from industrial machines. The modern robust control studies have shown that certain types of robot faults can be overcome with compensation of perturbations [6]

Methods

Results

Conclusion