학위논문 (석사)-- 서울대학교 대학원 공과대학 기계항공공학부, 2017. 8. 윤병동.A gearbox is one of the critical components in rotating machinery. Timely prediction of gearbox faults become of great importance to minimizing unscheduled machine downtime. Most of gearbox diagnosis studies are focused on the development of gearbox diagnosis algorithms using costly vibration sensors. However, vibration sensor cost matters in some applications, thus pushing to the use of a low-cost accelerometer, such as a knock sensor. This study uses a planetary gearbox with a knock sensor, known to be cheap and good for application (i.e., diesel engines) to detect high frequency.
This study develops a quantitative sensor evaluation process for fault diagnosis. The performance of the sensor is evaluated in terms of vibration performance and fault diagnosis performance. Vibration performance evaluates the sensor's noise level through an experiment using an electro-dynamic transducer. The fault diagnosis performance is evaluated by analyzing the vibration signal obtained from the faulty gear through gearbox feature engineering to check whether the fault has been separated or not.
In this study, two ideas will be proposed. First, some quantitative metrics will be used to evaluate the performance of the sensor. The vibration performance of the knock sensor is comparatively evaluated with the signal-to-noise ratio (SNR). The stable frequency range of the knock sensor for the fault diagnosis is defined based on the SNR value. From the point of view of the fault diagnosis evaluation, fault separation capability is carried out by probability of separation (PoS) and Fisher discriminant ratio (FDR). Second, a new application of the base signal of feature used for the fault diagnosis will be proposed. The filtered signal obtained by the alternative signal processing method(i.e., autoregressive-minimum entropy deconvolution (AR-MED) and spectral kurtosis (SK)) in the case of no tachometer is used as a difference signal. Analyze the frequency range and periodicity of the fault signal to determine the availability of the feature calculated with the newly applied differential signal.
Two case studies are presented to demonstrate the effectiveness of the proposed sensor evaluation process and metric: 1) one-stage planetary gearbox in a wind-turbine rig tester and 2) a swing reduction gear (two-stage planetary gearbox) in an excavator. It is concluded that a knock sensor can be used for the fault diagnosis of a gearbox.Chapter 1. Introduction 1
1.1 Background and Motivation 1
1.2 Scope of Research 2
1.3 Structure of the Thesis 3
Chapter 2. Technical Background 4
2.1 Fault Diagnosis in a Planetary Gearbox 4
2.1.1 Vibration Characteristics of a Faulty Gearbox 4
2.1.2 Signal Processing Methods 6
2.1.3 Features for Fault Diagnosis 9
2.2 Overview of Sensor Selection 11
2.2.1 Specification of Accelerometer 12
2.2.2 Selection of a Knock Sensor 14
Chapter 3. Knock Sensor Evaluation from the Viewpoint of Vibration Measurement 17
3.1 Conventional Sensor Assessment Method 17
3.2 Signal-to-Noise Ratio (SNR) 18
3.3 Method of Estimating the SNR 19
3.4 Results and Discussion 20
Chapter 4. Knock Sensor Evaluation from the Viewpoint of Fault Diagnosis 22
4.1 Review of Fault Diagnosis 22
4.1.1 Model-based Methods 22
4.1.2 Signal Processing Based Methods 23
4.1.3 Discussion 24
4.2 Fault Diagnosis using Two Types of Difference Signals 25
4.2.1 Definition of Difference Signal 25
4.2.2 Methodology for Estimation of the Difference Signal 26
4.3 Results and Discussion 28
4.3.1 Description of Experiments 28
4.3.2 Comparison of Fault Diagnosis using Signal Processing Results 33
4.3.3 Comparison of Diagnostic Performance using Quantitative Metrics 49
Chapter 5. Conclusions and Future Work 54
5.1 Conclusions and Contributions 54
5.2 Future Work 55
Bibliography 57
국문 초록 63Maste
